This is where the overprotective nature of American parenting comes to bite you: your kid will be fine playing with other kids outside, why not… do it?
That near as I can tell no one lets a kid out alone is indicating how big a problem it really is. The most I’ve seen here is when they’re paired up and 12+, and here is one of the safest places in the county in a very child friendly place, literally 2 blocks from the police station - and the police here have some of the best reputations in the country.
But it does mean that a lot is subject to opinion. And once you're on the radar, how do you get off? How do you prove you're a good, safe, responsible parent when the judging worker believes otherwise and has some authority to make that fact?
No, I am not arguing that. I am arguing that the system allows for it to happen a non-zero amount of the time.
And as a consequence of that possibility, the fear of it happened is a reasonably motivating factor in parent behavior.
Which isn't something we can (or should) probably fix. But is something that is.
Here in the bay area, I only know 1-2 areas that are like that, and even then you'll only see teenagers. Might end up moving if one is local! I'm in the lower peninsula area.
The PNW isn't for everyone, but we know how to get outdoors at all ages :).
Put rails on it with teacher or parent supervision, so it doesn't get out of hand and the worst excesses can be avoided.
But if children can't navigate social situations... they grow up into the adults we are literally talking about.
(Said as someone who had a difficult time socially as a child, and put in and continue to put in considerable work to improve myself)