I' looking for a fic that I can't find anymore. I'm quite sure that I read it on AO3.
Steve brings Bucky to the Tower and Bucky is quite nervous about meeting Tony (because of Tonys parents). But Tony isn't there and Bucky relaxes a bit. There is a boy and Bucky has no problem to bond with him - but that boy is Tony and no one of the Avengers thought to tell Bucky this fact.
It would be great if someone could point this story out :)