Japan has entered the chat... In Japan, children are encouraged from early age to be independent. They even take the subway and bus by themselves, albeit it's significantly safer there than in other parts of the world. Still though, I think people in America have gone off the deep end.
Its funny, because I see young-ish kids alone or in small groups walking around all the time in Brooklyn. Between 2:30 and 4:00 PM the sidewalks around my apartment are choked with unaccompanied kids.
There's packs of them that transit their way to local skate parks near me.