@kyrex agree with you, even if he disappeared all traces of his family, making it impossible to know how many died/disappeared, SOMEONE had to have seen the kid leaving the neighborhood and recognized him, at the very least I doubt they have forgone cameras because of the heroes
Could be the world being focused on the heroes' side, therefore ignoring or "not seeing" the bad things of society other than criminals (poverty, homeless people, etc.), but as you say, the fact that a lone kid was not picked up by anyone until All for One found him, not even a passing hero, makes it seem completely impossible.