It is incredibly common for kids to be alone in cities in the US. I can look out my window right now and see 2 children playing in a park with no supervision.

On my train commute every morning there were school children who get off at my stop because it’s where their school is. Their rides happen at reduced fares as well.

The trope rings very false to me and seems to be about one particular demographic (white and suburban).

If there is an increase in over watching our children it’s because we’ve over indexed on cars, not the reverse.

There have also been cases where families were threatened with/by CPS for letting their children outside without supervision. It's good to know that attitude is not universal, but it does occur.

Those cases are newsworthy, because they are newsworthy.

As kasey_junk implied, this sort of over-protectiveness is not universal in the USA. For example, NYC provides all students that live further than 1/2 mile from their school with a discounted public transit card (soon to be free). While very young kids are rare, tween and teen students can often be seen unaccompanied on mass transit. And even more often walking alone or in groups without parents. No one bats an eye except possibly to complain a bit about the groups of boisterous kids blocking the sidewalk :-)

> no American parent would dream of letting their children go out alone and recently, this includes even children in their early teens

This is, AFAICT, mostly a white suburban “middle-class” (mid-high income working class, including proletarian intelligentsia, really) attitude, rather than something that applies to all American parents.

Along with the other replies, you're right. I will say though, when we're talking about car culture, white suburban middle class types are ones to mostly support it.