Yeah like in goodfellas when Henry and Tommy are selling smokes and talking to eachother, we see that they'll be friends later on. Unfortunately we didnt see much of them as kids, but in other movies like sleepers etc we get a good luck at brooklyn kids as kids and as adults, they're just as ruthless at both stages in life
I agree that once upon a time in america is the apocalypse now of mafia films "I like the smell of the streets, it gives me erections"