When I was 8, the treehouse that we boys built out of materials that housebuilders left lying around was 50 feet up there. By the time I was 9 we had 3 of them at different heights. My grandmother visited and was surprised how high I was.
I bicycled far away, explored the woods, got lost sometimes for an hour and figured out the way back, got my legs stuck in mud and couldn't get out, etc.
When my son was that age, I would have him play at a playground a block from where I lived after school for an hour. This is a quiet residential neighborhood, not a big urban environment. One day a very young CPS woman with a foreign accent because no one wants the repulsive job, phoned me, saying there had been a citizen report. I was so surprised that I agreed to never have him play there alone again.
1) What difference does it make if he's alone or if there's another kid there?
2) Since kids aren't supposed to play at playgrounds nowadays, why doesn't the City surround any new playground it builds with a barbed wire fence and a sign: "Playground. No playing. Or we will steal your kid and you'll spend $10,000 for a lawyer and after interrogating your coworkers and relatives, if we can find anything about you like drug use, you'll never see them again."