A/N: If you haven't already, please read Love You Forever by Robert Munsch. Or, there's a bunch of audio versions of it on youtube. Just. Go.
...
"That's a good boy, now open up for daddy" Tony says, as he offers Steve a spoonful of baby food.
Steve opens his mouth, and giggles as Tony pretends to fly the spoon into his mouth. Steve knows it's probably the most cliche thing to do, but he appreciates the effort from Tony. Heck, he appreciates that Tony didn't flip out when he first told him he wanted to be his baby.
"Good boy!" Tony praises Steve as Steve swallows the food.
Steve should feel ridiculous. He should feel humiliated, and emasculated. He's Captain America. And yet he sits in a high chair, being treated as an infant by Tony Stark, and wearing a onesie with a diaper underneath. He doesn't though. He feels happy. He feels accepted. He feels safe. He feels loved.
"All done?" Tony asks, wiping to corners of Steve's mouth with a napkin.
"Yes daddy" Steve replies. Tony puts Steve's pacifier in his mouth. He climbs down from his highchair, and takes Tony's hand, allowing himself to be lead to the living room. It's moments like this that Steve almost wishes he never took the serum, that he was still small and weak. Small enough for Tony to hold.
The living room of Stark tower is lined with various baby toys. Bright colourful ones that light up, make sounds, and move on their own.
Steve comes from a simpler time, but Tony makes it his responsibility to introduce Steve to all the cool new toys of the 21st century. Steve doesn't even have to pretend to be delighted with them, he sincerely is. He lays on his tummy as he watches bright plastic fish swimming through a fake fish bowl. He presses down on a bright blue button and they light up for him.
Tony loves watching him like this. The big strong Captain America, so vulnerable. Sucking contently on his pacifier, fascinated by a simple baby's toy.
"Daddy look," Steve says, pacifier still in his mouth, as he points to the fish.
"Cool, eh little guy?" Tony says as he sits down next to Steve and pats his head. Steve always finds himself surprised by how well Tony takes on this role. He's not only Tony Stark, he's Iron Man, he saves the world frequently. He describes himself as a genius, billionaire, playboy, philanthropist. He's Howard Stark's son. But he treats Steve with such affection, he's so careful, so loving. He lets out a small yawn and nods.
"I think it's about nap time for you" Tony says, placing a hand on Steve's back.
Steve frowns a little. He pulls his pacifier out. "Daddy?" he says, looking up at Tony.
"Yes?" Tony asks, rubbing Steve's back.
"Can you read to me first?" Steve asks.
"Of course baby, why don't you go pick out a book?" Tony asks, his hand resting on Steve's back.
Steve smiles, and jumps up. He runs to the bookshelf, which Tony kept stocked with childrens books just for occasions like this, and grabs his favourite.
He toddles over to Tony with the book.
"What do you got there little guy?" Tony asks, and Steve presents the book to him, "Love You Forever, are you sure?".
Steve nods. It was one of the first books Tony had read to him when the whole thing started. Tony insisted that every baby in the world owns at least one copy of it. There may not be a guide to becoming a parent, but Love You Forever was as close as it got. Steve shed a few tears the first time he heard it, and Tony got a little choked up at seeing him like that.
"Okay little guy, lets get you all settled in, then we'll read this" Tony says, he takes Steve's hand and leads him to their room. Tony had thought about getting a custom built crib, but he didn't want to give up sleeping with Steve clinging to him.
They crawl under the blankets together, and Steve lays his head on Tony's chest while clinging to his side. Tony wraps one arm around him, and uses the other to support the book, the glow of the arc reactor lighting up the book.
"Read daddy," Steve urges.
"Hold on baby, I'm going" he says, as he tries to open the book with one hand. Steve grabs the other side of the book, and helps him support it.
"I'll help daddy!" Steve declares.
"Thank you, my baby. Okay, here we go," Tony says, readying his voice for reading, "A mother held her new born-"
"A DADDY, daddy" Steve says. Always finding a way to relate the books to himself.
"Okay, a daddy held his new born baby and very slowly rocked him back and fourth, back and fourth, back and fourth. And while he held him he sang- I'll love you forever, I'll like you for always, as long as I'm living my baby you'll be" when he finishes singing the last part he places a kiss on Steve's forehead.
Tony continues on with the book. Steve loves it when Tony reads. He sings in all the right spots, and he makes the funny voices in all the right parts (Steve laughs every time when Tony loudly reads "this kid is driving me CRAAAAZY" in his most ridiculous voice that he reserves just for Steve).
Steve's eyes grow heavy, but he stays awake for the whole book. Right to the last line. "I'll love you forever, I'll like you for always, as long as I'm living my baby you'll be" Steve sings. Steve isn't the best singer, and he doesn't like singing. But he does it for Steve, and Steve loves him for it.
"You made it all the way through" Tony says softly, kissing Steve's cheek.
"Daddy stay with me" Steve says, his eyes closing.
"Of course baby," Tony says, pushing the pacifier back into Steve's mouth.
...
Tony is gone when Steve wakes. He's groggy, he's hungry, his diapers wet, and he wants his daddy. He lets out a whine. He spits out his pacifier, "Daaaaaddy!" he calls out.
"Should I alert Daddy you've awakened, Mr. Rogers?" JARVIS responds to his whines.
Steve is agitated by the machine. He doesn't understand it. He doesn't like it. He makes an annoyed whine, and calls out again "DADDY!".
Tony finally runs in, his shirt dirty, obviously just coming from working on a new feature for the suit or who knows what. He looks worried, "Yes, baby, are you okay?".
Steve's lip trembles, "Daddy," he says, holding his arms out.
"Oh, come here" Tony says, sitting down next to him and taking the boy in for a hug.
Steve rests his head on Tony's shoulder.
"Now, whats wrong baby?" Tony says, his arms still wrapped around Steve.
"You left, and I'm hungry, and wet and-" his voice cracks and he lets out a small sob.
As much as Tony hates seeing him so sad, he loves how he's completely let his guard down. He's being completely himself. "I'm sorry I left you baby, I had work to do" Tony says, rubbing Steve's back.
"You're supposed to stay" Steve says.
"I know baby, I know" Tony says, "How about we get you cleaned up and fed, and then we'll watch a movie. You and me. Your pick. And we'll cuddle, lots of cuddles".
Steve smiles, "Okay daddy".
Tony lays the changing mat down on the bed, and gathers all the supplies.
"Lay down little guy," he says to Steve, who follows his command and lays down on the changing mat. Tony unsnaps the snaps on the crotch of Steve's onesie, and pulls it off so he has access to Steve's diaper. Tony loves seeing him like this. So vulnerable. He's completely opened himself up to Tony. There was a time when Steve was embarrassed to even be seen in a diaper. Tony had to coax him into letting go, and finally using them. Now Steve uses them without thinking, and isn't shy about letting Tony know when he has done so.
He opens the tapes on the diaper, and listens to it crinkling as he does so.
Fuck Tony thinks, as he opens the diaper. Steve's rock hard, but not from sexual attraction. From the excitement of being babied in such an intimate way. Tony has tried to get sexual with Steve when he's in baby-mode, but he's in a completely different mind set and it doesn't end well. It feels dirty Steve always says.
Tony thoroughly cleans Steve's crotch. "You're being such a good boy for daddy," Tony comments. Steve beams up at him, proud of himself.
Tony tapes on a fresh diaper around Steve's waist. But leaves the onesie off, because Tony finds him fucking adorable in just a diaper.
He helps him up, and pats his bum. "All good, little guy!" Tony says. "You wanna be a good boy for daddy and throw this out?" he asks, handing him the rolled up dirty diaper.
"I can do it!" Steve says, and he waddles off to the diaper disposal to show daddy what a good boy he is.
"That's my boy!" Tony says, "Now, what do you want to watch?".
"Tarzan!" Steve says, as they head for the living room, Tony carrying their fluffy king sized blanket with him.
"Again?" Tony asks. Steve went on a Disney binge after Tony introduced it to him, and has been hooked on Tarzan ever since.
"It's my favourite" Steve proclaims.
Tony lets Steve fiddle with the DVD machine as he prepares him a bottle. "I got it!" he hears Steve call, "Hurry daddy!".
When the bottles finished heating up Tony sits down on the couch next to Steve, who immediately curls up on Tony's lap, draping the blanket around both of them.
As the movie starts Steve latches onto the bottle, and Tony holds it steady.
This works, Tony thinks. He loves Steve in every way possible. He loves him as an adult, and he loves him when he's a baby. He stares down at Steve, watching him gulp down the milk. Steve looks up at him and blushes, smiling around the bottle. He releases the bottle from his mouth, "What daddy?"
"I love you, so much" Tony says. Because he does. He really does.
"I love you too, daddy" Steve says, smiling.