Tony get's turned into a 1 year old by weird goo that got on him during a mission and now Steve and Bucky both care for the new infant Tony *He may be baby size but still has his adult mind and understands what's going on*
What if Steve gave sperm back before he froze? What if by accident in 1999 they used his sperm and then once the woman finds out who the dad is, sends her to him at 11 years old.
Now it's 2021 and she's nearly 22. She meets dad's best friend Bucky and instantly feels a connection. They hide it because, 1. Age and 2. Steve Rogers.
What if they cannot hide it anymore?
What will Steve think?
*Natasha and Tony Stark are alive and so is Pietro* :)