bucky was going through tony's stash of random stuff that he kept away and he comes across this cool blue bottle with a big CAUTION on the front and he thought that he'll experiment it out on himself and the others so he slipped it to everybody's drinks (except for bruce) and when they all drank it, they turned into confused toddlers and bruce coming home with arms full of grocery bags and going "what the fuck happened here"
Bruce would walk in like this:
Bruce, naturally, would have to find the reverse serum for this, so he’d immediately gather up all the kids & bring them to the lab. The serum they drank is temporary, but he’d rather find the cure soon so he wouldn’t have to deal with a whole group of toddlers for too long. Well, toddlers with superpowers.
Oh my god, imagine trying to catch Pietro. Or Sam, who’s managed to find his suit & is now precariously flying around at a bit too high of a height. And imagine a tiny toddler with a super-powerful bionic arm. Good luck getting anything out of his hand.