In the US one of the big problems is a culture of legal liability for every possible thing, and a general culture of fearfulness, excuse-making, and ass-covering instead of allowing moderate informed risks and dealing responsibly with the consequences. If you have too steep a slide, some kid is going to fall off and the parents will sue and bankrupt your town. If you let kids ride the bus by themselves, 1 kid in a million is going to get kidnapped and the parents will sue. Etc.
But there are surely other contributing factors: more families with 2 working parents (and more single parents) and in general less adults “hanging out” with an eye on their neighborhoods, a general degradation of community relationships and civic institutions, smaller family sizes (it’s much easier to chaperone 1 kid than 6), more middle-class angst about maximizing children’s future earning potential, more media attention on rare tragedies, communication improvements leading to less spontaneous social gatherings and more virtual socialization, increasing reliance on car transport and inaccessibility of unsupervised play spaces (especially undeveloped land), etc.
I think this is a big one, and not just rare tragedies but distant ones. 40 years ago you heard about the bad things in your village, now the 24 hour news cycle feeds a constant stream of fear from all over the world.
Yes there is a trend to 'protect' kids from everything. But in my country there is a clear counter-culture advocating agianst what they call 'rubber stone' society where everything is done to avoid possible danger.
There are now ads running on TV saying 'let boys be boys', let them climb trees, go out and explore etc...
I now live in the US and have kids about the same age.
The issue is not homogeneous culture or any other thing people with no brains come up with, but traffic density, at least in my case.
Where I used to live we could roam without having to cross dangerous streets. Where I live now, there's traffic everywhere and cars don't give a shit about people on foot, so my kids do not roam.
When I was a kid, we used to have vast areas to play safely. I just looked on Google Maps and the cross-country ski route we used to regularly take on weekends is 4 miles long. We had to cross ONE street. I used to bike about 10 miles one way, by myself, when I was a little older and keep on bike lanes the entire trip.
We also used to have large play areas in the backyard of every home I ever had. The bigger ones were the size of a typical New York borough block. We didn't have to leave our homes to get to a playground, or a park...we had one right outside of our door.
Obviously this sort of thing is easier to do / plan for when the entire country has less people than the city of New York.
(weird really - can you do that for killing people by any other means?)
My wife and I have semi-seriously considered moving to northern Scandinavia for both this reason and its comparative likelihood of remaining a decent (well, bearable, if only just) place to live in a clathrate-gun scenario.
There was a case not far from where I live where a driver turning right mowed down a 4-year-old child walking with his grandmother on a CROSSWALK. He wasn't running or anything like that, just crossing the street. The child died. They didn't even charge the driver. Fucking ridiculous. It was 100% the driver's fault. New York Times published an article written by the child's mother who questioned the logic of first of all call it an accident and second of all how the driver wasn't charged with anything, not even reckless driving.