I noticed this 25 years ago. We lived right next to an elementary school that had a playground and a baseball field, we moved in in 1988. It sat empty all the time except who organized softball was played, and kids never used the playground equipment except during recess. When I was a kid in the 60s and 70s there would have been a ball game going on every day while the sunlight allowed, and football would have been played in the fall. I actually drove by our old house a few months ago, they have built on the old ball field, now just more classrooms, was sad to see it....
My brother and his wife lived in Beverly Hills for awhile in the 70’s. I went out there to visit them. The first thing I noticed was that there were no kids outside. I asked him why and he said parents arrange to have kids visit one another. He said that everybody was afraid of kidnapping.