I agree with this for the most part but it doesn't explain everything.

The town I grew up in has a lot of areas that are conducive to children roaming; low traffic speeds and volume, separated sidewalks, parks, green spaces. As kids we ran around freely. The traffic volume and patterns haven't really changed at all and as a whole the community drives pretty slowly, nobody seems to be in a hurry. Yet you never see kids out anymore. Where did they go?