Look at the way our cities are built. I live in a grid based streetcar suburb and my kids can be let out feral. If you live in a modern subdivision ... Good luck. The roads are too big, and there is nowhere for kids to go. Meanwhile, my local city has free lunch at the park for kids every day during the summer and kids can go unaccompanied. I see tons of kids out riding bikes and walking by themselves.

Impossible in modern developments. You'd have to cross a six lane road with 50mph traffic to get anywhere not safe.