I don’t think you can profile this as American. Are they conservative suburbanites? My kid walks to/from school longer than that. Many kids take public transit in big cities. Rural kids may ride a motorbike much further.

Well, it is a pretty American thing for this to be the case. Americans have been arrested for letting kids walk 500 meters on their own before (in certain neighborhoods)

Like Europe, the US has a pastiche of laws across states and municipalities, and varying levels of enforcement. My state has laws protecting free-range children.

You’re probably right that only in the US do people freak out over unaccompanied kids, but I wouldn’t say that’s true of most of the country.