Steve and Tony hadn't been married long before they adopted Peter. Only a couple years into their marriage had Director Fury contacted them in need of help on a case. What they didn't know was that the 'case' wasn't a real case at all. You should've seen the look on Tony's face when Fury asked him to be the father of one newly orphaned Peter Parker.
"Nikki, I've done a lot for you, I really have. I clean up after you, I save the world for you, I risk my life for you, and in return you're asking me, me of all people, to adopt a child?"
"His parents were SHIELD agents and he has no other relatives to stay with. You and Steve could do it, this isn't a favor I'm asking, this is a mission."
"My God, you've taken too many blows to the head..." Tony muttered under his breath.
"Tony, what other choice does the boy have?"
It was to Steve's surprise that day when Tony came home with another male.
The male was an infant, sucking it's thumb, and crying loudly, but still. Steve walked into the lounge with wide eyes.
"Make it shut up," Tony groaned, holding the baby from under the armpits. Young Peter dangled limply in Tony's hands, his cries becoming more and more unbearable to the billionaire.
"Tony! What the-?" The blond cut himself off, reaching out for the child. "What are you doing with a baby?" Steve questioned while gently bouncing the crying orphan.
"Steve, there's no easy way to say this, but-" Tony took a dramatic breath, "I was pregnant all along."
"Ha-ha," Steve mocked through squinted eyes. "What's really going on here?"
"Director Fury wants us to keep the kid. Apparently it's family is all dead and stuff. They were SHIELD agents, so they couldn't have just shipped the kid off to the nearest orphanage." Tony explained all in a single breath.
"So...we're keeping him?"
"So it seems,"
"What's his name?"
"Peter. Peter Benjamin Parker."