It's a related cultural factor. The more we build our outdoor spaces to accommodate cars over people, the more notable it becomes when there are people in them.

That doesn't really explain the differences though. Car culture and design was as prevalent in the 40s-90's too, which basically defined the ideal of suburban sprawl. However, those spaces were also filled with children, often literally playing sports in the streets.

Parents and elderly at the time had grown up with playing in the street, so they could hardly be bothered by it. Now we have the next generation that has only known cars (oddly enough probably the ones that played in the street).

Yep! I blame the rise of 24 hour news and the need to spread fear mongering in the name of ratings. I think it coincides nicely with the problem.

car dependent development takes away children's independence ->

people are not used to seeing kids outside ->

they freak out when they see an unaccompanied child

Maybe if she’d been doing her homework in the car on the front lawn, it wouldn’t stoke such fears?