It finally happened. It was the perfect moment. Their parents were out, they were alone in the house, and Starshine and Blue Monday were a filly, and a colt, respectively. Monday was the one who learned about it. “Hey sis, c-can I tell you about something?” he asked nervously.

“Sure, what is it?” Starshine replied. The white filly with a golden mane was already softer and rounder than her big brother (by 1 year) whose mane was a darker brown, and fur coat was a rich blue.

Monday listened around to see if their parents could hear, then said, “I found out how foals are made!”

“Yeah, in a filly’s tummy, right?” Starshine asked hesitantly.

“No, I found out how ponies make them!” he said excitedly, “It’s really weird!”

“What do you mean?” she asked skeptically.

“W-well, the book said… you know how the foal comes out, right?” he asked tentatively.

Blinking, Starshine had to shake her head. She’d never thought of it before.

“Well, you know where you pee?” he asked in a tight whisper.

Her eyes widened at his bold language. “Y-yeah?” she said, trying to pass it off as brave. Why was her brother asking about that?

“That’s where the foal comes out!” he declared. “You know how you don’t have a… a penis?”

“I… yeah I don’t but… how does the foal…” she said anxiously, looking at the smooth curve of her belly.

“Your thing gets really stretched, like a rubber band,” he explained, “I saw the drawings of it in a book in the library.” Blushing he added, “N-nopony saw me take it out to look at. But the foal just… squeezes outta you back there, like you’re a tube of toothpaste!”

Starshine laughed, saying, “That’s impossible. He has to come out your mouth or something. He’s in my belly, remember?”

“Well, that’s your… thing down there,” he said uncertainly, “It’s a special mouth, for foals to come out of.”

“I think I’d know if it was a mouth,” she said irritably, the mental image not necessarily unpleasant but very weird. “I can’t open a mouth down there or anything.”

“No, it’s a… oriface,” he replied, “It just stretches open, when you push the foal out with your belly. Like a… like a thing I don’t know.”

“Well… why would I wanna just… stretch open a… oriface back there?” she said, her tail twitching lower.

“I dunno, but that’s what happens,” he said, giving Starshine a cautious look. “You’re a filly,” he said, “You could get a foal in you.”

“I… yeah,” Starshine said, blushing shamefully. “I don’t wanna but it… it could happen I guess. How would I even… get a foal in me in the first place? Does she just start… growing in there?”

“Sort of,” he said mysteriously, “You don’t only have a mommy, remember!”

“So my daddy…” Starshine prompted.

“He puts a foal in there!” Monday said, “Well I mean he puts something called semen in there, but that unites with your egg and makes a foal.”

“My egg?” Starshine asked, scrunching in confusion and vague disgust.

“Y-yeah you have eggs hiding in you, just like a chicken, but you don’t lay them,” he offered, “E-every filly of every creature has eggs inside them. It’s just chickens have really big ones that they lay.”

“That’s… okay that’s really weird,” Starshine said nervously, “I have e-eggs in my tummy?”

“Y-yeah,” Monday admitted, “And… if they hatch in there, then you’ll have a foal. A-and you’ll be a mommy. And you’ll push the foal out between your legs.”

Looking at the mysterious pocket between her legs, Sunshine said in dismay, “Oh, it’s wet again.” Blushing and facing Monday she said, “I, ah, uh, mean…”

“S-so my seed has to get in your belly,” he said, distracting her from that embarassing conversation, “My seed I mean… any colt’s seed will make your egg turn into a foal. Then you grow a foal inside you until you have a really big tummy. Then you squeeze her out between your legs.”

“I… I keep getting wet, thinking about squeezing out between my legs,” she said in the confidence of a filly losing herself in lust, “I could really fit a foal in there?”

“Yeah, and my seed has to get inside you, first,” the eager colt told Starshine.

“O-oh,” Starshine said noncommitally.

Gulping, he continues, “And if that seed gets inside you, b-between your legs, then you start turning into a mommy, and your foal starts growing in your belly, because my seed… swims around inside you, and finds your egg.”

“S-swims around inside me?” she squeaked.

“It… yeah you have a special place in there that a foal goes,” he said, “And if I put my seed in there, it… stays in there, for 3 to 5 days. Sort of swimming around, until… it finds your egg.”

“This is so crazy!” she said, shaking her head, “A-and you read this?”

“Yeah I did, I wanna… put my penis inside you,” he said, making her blink in surprise. “W-where the foal comes out,” he said, “That’s where I put my penis inside, and then if I ejactulate, it’ll be really deep in you, to put the seed in your belly.”

“W-why?” she asked in fear, “I… I don’t wanna be a mommy.”

“I don’t wanna be a daddy,” he replied with a shrug in his ears, “I just wanna… feel what it’s like. The book had the picture of a stallion going into a mare down there, and it… looked really good.” Swallowing, Monday admitted, “I’m just kind of curious what you would feel like… in there. And you’d be able to feel me in there too. You wanna… find out what it feels like to have a penis inside you?”

“I… I wanna say no,” she whined in frustration, “But thinking about it is making me wet down there, and you’re gonna put your penis in there?”

“Just to feel it!” he said pacifyingly, “Just… aren’t you curious too? What a penis feels like?”

“I… shouldn’t be,” she said, blushing at that bobbing rod again, “But I… I do. H-how are you gonna put it in me?”

“Lay on your back,” he suggested, “That’s what the book said. Then I just stand over you, and… push my penis in.”

“Yeah, I’m a colt, and that means I can make the seed that turns you into a mommy, if it gets inside you,” he said casually squirming in place so nonchalantly. “T-the book said the seed comes outta my penis.”

She seemed speechless about that, staring at his penis already drooping beneath his body, swinging there. “Yeah that’s why I have a penis and you don’t,” he said, trying to put it off as no big deal. “I’m supposed to put my penis inside your vagina, a-and then thrust it inside you. Then I ejactulate, which means the semen comes out of my penis.”

“Thrust?” she asked.

“Yeah I have to… slide it into you and out of you. And keep doing that,” he said. “I can’t just ejactulate right away. So you won’t become a mommy, if I don’t push in and out a lot. I need to do that thrusting before my penis will do it.”

“Oh, oh so… you can put it inside and I won’t be a mommy?” she asked.

“Yup,” he said happily, “We can both feel it that way, and as long as I don’t thrust, I won’t put seed in you. I just can’t do it at all unless I do the in-and-out thrusting.”

She rolled onto her back, hooves curled over her chest, saying, “"Okay, I’m… oon my back!”

“Oh Starshine, I… thank you so much!” he said emotionally. “I wanted to try it, and I didn’t know if you would let me. I… I really can try it?”

“I dunno,” she said with a curious tingling heat welling up in her belly, finding it hard to think with distracting things like her brother’s penis in front of her. “I… I’m curious too. Just to feel it, I mean, not ejactuate or whatever. If you can actually put your penis inside my belly, that’d be so… weird.”

“Okay, I’m…” he climbed over her, leaning against her hind legs, and lowering his penis to softly part her folds. Starshine inhaled sharply at that, an intense ache flowing from between her legs, like an itch being scratched. Starshine’s penis was so soft, but still hard somehow.

“Uh huh,” he said hopefully, just sort of wedging her nether lips apart with the head of his penis, then pushing strongly against her and… sliding right in! Her breath grew quicker, and more urgent, as she just wrapped around him, and his penis opened her up deeper and deeper.

He did stretch her wide, it felt so weird! She felt him sliding in there! Staring at that boy pole sliding into her, she said, “Y-you’re going really deep."

“Yeah you’re… really deep,” he said distractedly, pushing until he’d hilted in his sister’s vagina. Facing each other, they both could see it happen. “You’re hot and… wet in there,” he said shakily, “So weird. I can feel it with my penis!”

“I can feel your penis too!“ Starshine announced in shock. "It’s this big… thing inside me.” she said, putting a hoof on his chest, “I didn’t think I’d be so… stretchy. It’s like I’m wrapped around you~”

“This’s when the stallion would… ejactulate,” her brother said, hugging her hips to his, her fillyhood so weirdly distorted, stretched like a rubber band.

“I can f-feel where you would,” she replied, touching her belly, where deep inside, a penis was pushing up into her squishing against her all the way in. “You’re not gonna ejactulate, are you? Your… your penis’s all ready to. If you did even a little…”

He started to slide in and out of her then, and her breath quickened and deepened. “This is the… thrusting you talked about,” she said warily, a hunger rising in her for that penis inside her that she’d never felt before. It was so… sliding, and hard! “T-to make the stallion ejactulate?”

“It’s hard to stop,” he said distractedly, not stopping. “I never… never ejactulated before,” he added, looking at her fearfully, “I dunno what it would even feel like!”

“Are you gonna?” she asked anxiously. He didn’t answer, just kept fucking her. She should have told him to stop. She couldn’t have a foal in her! She was just a filly! Their thrusts reached a primal, steady rhythm, and they were staring at each other, but lost in the feeling of his penis sliding in her vagina.

She started wanting it. She started really wanting it. There was a tingle growing in her belly, right where he was sliding. It made her heart beat fast. It made her long for him to push deep inside her, which he did again and again. She didn’t want a foal, did she?! She didn’t want to stop though! She couldn’t think with this rushing tingle!

“I want it,” he said, eyes full of lust and fear, “I don’t wanna stop.”

“I didn’t think I would want it this much,” she replied, eyes wide as she stared at him fucking her. “All I can think about is…” she humped up against him, prompting him to thrust faster. “How you feel in there. You keep sliding, with those… thrusts… want you inside me more and more.”

“I don’t wanna stop,” he repeated, humping strongly into her, while her legs wrapped around behind his. “Am I gonna put foals in you?” he asked anxiously, “I don’t wanna stop!”

“Want you inside me!” she cried out in passion, humping right back against him, their hips earnestly pumping as that penis shoved deep again and again. “I’m gonna make you ejactulate!” she squealed, frightened, “It’s gonna swim in me! You’re gonna… make me a mommy!”

The tingle overwhelmed her, and she fought not to squeal because then maybe he’d stop! “S-something’s!” she squeaked, and then everything started squeezing in there! It blasted through her body in mind numbing rushes of pleasure. She just bucked against him spasmodically as he fought to thrust into her passage that she couldn’t stop squeezing. It felt incredible! It was just rushing through her, like lightning!

Soon they were just dazedly humping together. She couldn’t think about anything but pushing their hips together, and getting that penis to slide inside more. She didn’t wanna be a mommy, but his penis made her only care about her vagina and the sliding. It was the most important thing in the world.

He pushed deep then, and she groaned at the feel of his penis suddenly shoving in there and staying there. The lack of sliding made her tingle rise up again, just the fact that he was twitching in there and… and he stared down at her in shock, saying, “It’s…”

Then hot pulses started to blast into her, right from where the swelled tip of his penis was pressed against her deepest insides. “I f… feel it!” she squealed, as it blossomed deep within her. “Stop putting it in me!” she cried, gripping his hips with her legs to pull him close. He just pulled her against his groin and kept doing it. She looked up at him in fear of what was happening to her, of how much she wanted it. Her fillyhood was… was filling with semen!

She… she started squeezing in there again, and it just happened to her. Every drop, he fired up deep into her, in places not even his penis had gone, just smearing all around her in there, like she was filling up with semen.

“I don’t wanna be a mommy,” she groaned, her cunny squirming in a smaller, but still breathtaking orgasm, as his penis stopped squirting, and he slumped over her, “It feels so good. You just made me a mommy! Oh I felt you putting it into me!”

“I couldn’t stop!” he replied anxiously, “It was tingling so much, and I just had to push it in you deep, and then it started squirting! I tried to stop, but it kept squirting!”

“Starshine, are you busy—!”

“Mommy! I can explain!”

“Well, is that what you’ve been up to lately? Making a foal with your friend?”

“I… I didn’t mean to!”

“Oh, you didn’t mean to, huh? Looks to me like this cutie (hair tousel) is balls deep in you right now.”

“S-sorry Mom—”

“It’s okay, Monday. Just enjoy yourself, and put a nice foal in my daughter’s belly.”

“It’s really okay?!”

“Sure! She looks like she’s enjoying it. You know you’re gonna be a mommy, right honey?”

“Y-yeah, but… I’m not trying t-to.”

“You want it, don’t you?”

“I… uh…”

“You keep doing it, even though it’s gonna put a foal in your belly. You tell yourself no, then you lift your tail for him. Has he cum inside you yet?”

“Y-yeah…”

“Happened to me before! And I gave birth to you! Isn’t that neat? Right down here, your little foal’s growing, and one day she’ll be having foals too.”

“I don’t know if I… have a foal I just… I felt him put the semen in there.”

“And you want him to do it again.”

“Yeah…”

“Well then, get to it! Dinner’s gonna be ready in fifteen minutes. How about you let him put a foal in you right now, then we can all get something to eat.”

“I–I wanna put a foal in her.”

“Then get thrusting! Go ahead. There you go…”

“Mommy, he’s—!”

“Feels so good, doesn’t it?”

“Y-yeah…”

“My little baby filly’s turning into a young mare.”

“Hnhh hnhh hnhh…”

“Mommy, can we…?”

“Have you done your chores, and cleaned your rooms?”

“Yeah!” (both)

“And your homework’s all done?”

“Sure is!” “Yeah!”

“Then go ahead, no problem! Ooh, you’re being an aggressive little colt today. That’s it, grab her good and get it in there.”

“Ah!! Mommy he’s… ah! Ah! Thank you, Mommy! Ah! Thank… you mom…mmy… hnnh hnnh hnhh.”

“It’s okay sweetie. Just let your female instincts take you, and get good and pregnant.”

“hnnh hnnh hnnh…”

“That’s my little mommy.”

She tried to hold back, but her belly was so massive, it had to squeeze! She couldn’t give birth now. She was in the middle of class! Starshine moaned as an intense contraction made her insides feel like they were stretching wide. A frightening urge was rising in her. There was a foal in her belly, and she had to get it out of there. She wanted to wait, wanted to hold it in, but it was time and she ever more desperately needed to squeeze this foal out just like Monday had said.

“Starshine, are you alright?” Mrs. Sunny said, trotting over to her. “Oh!” Starshine’s teacher declared in shock, “You’re giving birth?!”

“S-sorry, I can’t stop it,” Starshine whimpered, only upright from how she was hanging onto the desk. “It just started n-needing to come out more today, and now it really needs to come out.”

“Oh, that’s perfectly natural, Starshine!” the teacher said with a smile, “It’s time for you to finally become a mommy!”

“I don’t want to become a mommy,” Starshine moaned, huffing in the throes of another urgent contraction, “Wanna keep it… in but I can’t stop squeezing!”

“You might as well just give into the urges,” Mrs. Sunny told Starshine, “If it’s time for your foal to come out, you won’t be able to stop until it does.”

“Ungh, it’s stretching me so big!” Starshine cried, not even aware that the rest of the class was staring at her at this point.

“I believe that’s your cervix,” the teacher explained, “Once it gets big enough, you’ll start to push the foal out of you.”

“I don’t wanna… push the…” she said, trying to push this foal out as hard as she could. It was intoxicating, the need to push like this!

“Well… you can sit the lesson out this time,” the teacher said sympathetically, “You just relax and give birth, for now. I’ll see how you’re doing after the lesson, okay?”

“O… okay,” Starshine said, squeezing her legs together as if she could close this… yawning cavern inside her vagina. The teacher did give the lesson, though a few were distracted from it by Starshine’s predicament. Starshine tried to listen to it some, but she couldn’t think about anything other than her belly, and squeezing it and getting the foal out. She started trying to get the foal out. She wanted it to happen more and more. She just tried to quietly contract and give birth out here in the middle of class.

It seemed like no time at all before the huffing, sweating Starshine lifted her head to hear the teacher announce, “Now I encourage all of you to stay after class. This is a rare opportunity to see a pony giving birth. Starshine should be finishing up soon anyway, if she’s been this far into it for the past hour.”

“What?!” shouted Starshine, “I’m not fin… f-finishagh…” she had to contract. “Not… finishing,” she groaned around the intense overwhelming stretching sensation in her pelvis. “It just… keeps… happening!”

“Clear out the desks, everypony,” Mrs. Sunny said, “Let’s give Starshine plenty of room. Make a circle.”

“Ew… why’s it all wet down there?”

“That’s her water breaking. The membrane that held the foal in a nice warm bath has broken, so that Starshine only has to push the foal out, not the whole big belly.”

Every foal was clustered around Starshine, staring with fascination at her belly or between her legs. She felt so on the spot, but she needed to do this so bad, it was all she really cared about.

“Oh, I feel a contraction starting!” said May, who was laying her hooves curiously over Starshine’s taut, gravid belly.

“Y-yeah,” Starshine said with a weak laugh, “It’s… really taking me over. I can… r-resist a little bit.”

“Oh, you want to do that?” May asked curiously.

“I… I want to give in and squeeze, I need to… contraction,” Starshine said in more and more of an urgent voice. “H-hurry up everypony feel my belly if you want I can’t hold back…!” Several ponies rushed forward, squatting on their haunches around Starshine, rubbing at her belly so distractingly. With an indulgent groan, Starshine contracted, her belly turning to steel in the hooves of the surprised students. “I-it’s stretching me so much!” she squealed as the foal sank in her birth canal, no as she forced it in there.

“Oh look!” somepony shouted, “It’s a… uh…”

“It’s a face!” May squealed. “Y-your baby’s coming out!”

With the help of a mirror, Starshine got the lovely image of her legs spread wide, with a little lavender foal whose nose and the tips of their forelegs were just sort of sticking out of Starshine’s distorted passage. As she heartily contracted, the foal slid out more, bit by bit. She was a mommy! It was her foal! And it was in her… in her belly! She had to contract, and squeeze, and squeal, and push.

“I wanna be a mommy…” Starshine groaned hungrily, staring at her still huge belly. It needed to contract, “My foal’s inside me…”

“See, one of the effects of labor,” Mrs. Sunny explained, “Is to cement your relationship as a mother. The more you push your foal out, the more you feel like having her out. You start wanting to nurse her, and care for her, and well… not have her in your belly.”

“I… I do!” Starshine said tearfully, fighting not to contract, “I wanna be a mommy so bad! I wanner to be a real pony and my teats are… are leaking I need her to drink them! I wanna see her… smiling at me! I want her out! I can’t hold her in I have to pushnnnnhhh!”

Starshine contracted, and arched up as the foal’s head slid the rest of the way out. She did nothing but contract then, contract and breathe. She felt the foal’s shoulders squeeze past her labia. Then she felt the foal’s hips. The foal’s hips were in Starshine’s vagina! They were slipping out! There was nothing left!

“S-she’s coming out!” Starshine declared, a powerful flex of her abdomen making her vagina stretch so gloriously one more time, before the foal’s hips slipped out, then the legs and tail just sort of slid on after.

“Ha… haha…” Starshine laughed breathlessly. It felt so good to have done that. She gave birth! She was a mommy! She caught her breath a moment, then an urge rose in her to check on the foal. Sensible, but she was only running on instincts at this point. Sitting up, she leaned over the bedraggled looking sopping thing, all slimy and messy.

“Oh, this is something to take note of, class,” Mrs. Sunny said happily, “New mothers will instinctively clean off their foals after having given birth.”

Starshine was licking her foal’s fur clean in long, systemic strokes, only pausing long enough to say, “I’m just getting her (lick) clean,” before going back to passively licking it. The foal was a filly, that much was clear from Starshine’s broad tongue finding nothing male between her foal’s legs. She blushed at this point, realizing that this was kind of… weird to do, but she kept doing it. Her foal was just so… interesting! She had to lick her, and pay attention to her, and there was something really special about this little little pony. She’d just come out of Starshine’s vagina!

Then cometh the afterbirth.

Starshine was beaming proudly as she’d managed to stand, and feel her daughter start nursing at her. It was really powerful, the thought of it being her daughter. Starshine kind of figured that… this must be why mommies are so weird about their kids. This filly was just… it was hard to think of anything else. The class gave their well wishes or jeers or whatever, and then Starshine was left alone with her foal, to rest together.