A lot of the comments make great points but honestly I think the biggest problem no one has addressed is the massive expansion in population since the 70s. Thi

A lot of the comments make great points but honestly I think the biggest problem no one has addressed is the massive expansion in population since the 70s. This has lead to much larger "towns" and suburbs where the sense of community is essentially gone. At best you might know a few neighbors on your street. So risk tolerance has gone down for a good reason. And when you see a strange kid out playing and you don't know who's kid they are, you're going to naturally worry about them and just assume the worst. Another factor too astutely mentioned by someone below is the car dependent nature of most non urban environments, especially in North America. I see lots of kids playing near their homes on their own in the neighborhoods I live in. Parents aren't too far away and they're with the other kids of the neighborhood. Maybe the safe distance a kid can travel on their own hasn't changed, it's what you could actually accomplish in that distance that has changed. Today's society, especially western society, is much less community focused. So now, not only do I not know what strange adults exist in my 200 home open air neighborhood with a single playground, none of the adults there know me either nor my family and therefore a perceived sense of risk and maybe even actual risk is higher that my kids are in danger. That's what happens when population explodes and population density increases. All that's happening is the West is finally experiencing what many Asian and Middle Eastern Countries already knew.