There are a lot less kids as a % of the population. My mom growing up in the baby boom had to stand in the aisle of her school bus (something safety doesn't allow anymore), but if she got on the bus just 4 blocks sooner she could have got an empty seat! These massive numbers of kids don't exist and so there isn't much to play with.
My kids are happy that the corn fields around our how turned into a subdivision just after we moved in because now there are kids to play with. However only about 1 in 10 houses have a kid (some have grandkids over on weekends - I didn't count that, and others were the kids live with the other parent half the time get counted half).
My suburban neighborhood has ~100 houses, and only two of them (besides mine) have children in them. Lots of grandparents, though, who briefly have children over around holidays. The landscape is dotted with parks but they're all pretty much always empty, except for the occasional adult exercising or walking their dogs. Our local school district is spread out over a huge swath of suburban land, likely because there are just not enough kids.
It's probably different in the city, where presumably more people are parent-aged. Almost all homeowners I know out by me are over 45 and their children are adults by now.