In China, I would see kids who must have been 7 years old running around the streets or on public transit without adult supervision.

It seems like a much healthier way to live than in constant fear.

depends. my kids school in china didn't allow me to let my kids bike to school without supervision. (well, actually, they couldn't stop me from sending them to school alone, but they would not let them out unless i was there to pick them up. (there was only one crossing on the route, and that was close to the school and didn't have a lot of traffic)

in germany on the other hand, there was a case where parents demanded a school bus for a 7yr old, but the court said the kids could take the public train to school on their own.

In the US, if you are in a residential neighborhood with a lot of kids, its also fairly typical for them to be out finding their playmates.

I would say if you're in a neighborhood where there's just like 1-2 kids, it may not be that typical. The kids parents might do more scheduled playdates.

Unfortunately in the US there are people that get annoyed about kids playing. And they are also the same kind of person that escalates things to the authorities / complains a lot about trivial things.

There's a Netflix documentary about one such sad case https://www.netflix.com/title/82018736