Granted the numbers are lower now than before but that’s because of various safety and traffic calming efforts. Seems like we should push harder on that front, so parents can feel safe encouraging their kids to just pop over to their friends place on their own.
https://reason.com/2014/08/19/august-2014-reason-rupe-nation...
Americans are split regarding whether there should be a law requiring 12-year-olds be supervised when playing in a park - no cars there.
As an European, to me this is absurd. At twelve I had a bus card and the privilege to go wherever, as long as I respected curfew.
But the numbers say its the actual white van going too fast on a four lane road (speed limit 45mph) next to the park. This isn't that much of a problem in older European cities.
The OP said that everyone is walled off by cars so they have a mindset of controlling their children, lest they get run over. You're saying that they're actually afraid of kidnappers etc., while they should be of cars. To me these points are contradictory.
In any case do you think removing cars will solve the problem? My guess is that no, because this mindset appeared decades after cars took over, and these things are actually not related.
Things like the sex offender registry "help" but don't at the same time. It's not something I ever concerned myself with ("I know the stats, it's usually a relative!") until someone encouraged me to do it while closing on a house. I'm now acutely aware of the fact that there are dozens of child predators within a 1-mile radius of my home.
I think a big part of this is just our risk tolerances change. We naturally want to protect kids, and looking historically we've taken safety to relative extremes compare to 20 years ago (and similarly before then). Its natural to want more security, and its obvious how it helps. But its not as obvious what we've given up in return.
Interestingly, I moved to Portland recently, and live mid way between suburbs and downtown; its fairly dense but mostly SFH or townhomes in my neighborhood, many businesses, some homeless. Kids of all ages walk to school and are... just everywhere, around here. Its quite normal to see people walking with their kids too. Its just got a really great mix of urban density -- you can walk to stores, bars, school. There's a few high traffic streets, but they are not large and the speed limit is 20mph. I think what this neighborhood has taught me is, while our risk tolerances are lower than ever, its still a bit of a design and culture choice to not let kids walk around. Its nice to see here, in Portland of all places, there's a bit of a counter trend going on. I hope its what the future looks like in other places (here and elsewhere) too.