When I was a kid... we were still able to go to the park alone or with friends, walk to and from school, and engage in a lot of unsupervised activities even as young children. A big part of that was that our friends were doing the same thing - there were kids everywhere. Some of those kids had parents, older siblings or babysitters around, so there were older, more responsible eyes watching the activity. As we've moved our activities indoors, and have restricted kids from unsupervised activities, the odds have again changed. It's not unusual to drive by parks in my town and not see a single person there, or to see one or two families present. If a child goes there alone, the odds are that the child will spend some time with no other adult or child present. That significantly changes the risk to a child.There's also the fact that as communities have become more dependent upon busing and cars for transportation to school, the "neighborhood school" may be quite far removed from the neighborhood. I'll grant, when I was a kid I rode my bicycle to school across a relatively busy, divided roadway - but that road has nothing on the type of traffic my daughter would face if she rode her bicycle to school. (She's still too young to do that even by historic measure.) The lack of sidewalks along the way would also make it very difficult for her to walk, even if she were old enough to cross that road unsupervised - or even if she were accompanied by a parent. And it's almost three miles away, about an hour to walk.
And that's with her going to a school comparatively close to home. Her "neighborhood" school isn't close to the neighborhood. Yes, there are schools that are closer than the default (including the one she attends), but you can't look at the @4.5 mile, @90 minute walk to school and tell me that the school board was concerned about walkable distances. My childhood school was not my neighborhood school - it was about a third of the distance from my home as my child's "neighborhood" school; triple that distance and I would have been taking the bus (public transportation, not a school bus) as I had to do during the winter. (My neighborhood school was less than half a mile away, an easy walk or bike ride down quiet, residential streets.)
So let's not pretend this is about individual choices, helicopter parents, smothering, etc. - and let's recognize that if we want to shift back to a culture in which kids play outside with minimal supervision, walk to school, etc., we're going to have to make a serious investment in recreating actual neighborhood schools and in providing a safe level of supervision while the numbers of children increase. Let's not blame individuals for societal changes that are well outside of individual control.