No. It’s because of shifting standards. The “can’t play outside” applies just as much in places with no more cars than there were 40 years ago (or even no cars at all for most kid -> playground routes)
The town I grew up in has, for 95% of kids, no more than 3 internal, slow roads to cross on the way to school. There’s more traffic, but only slightly so - most cars drive away from town, so despite much more traffic in general, inner roads are only slightly more crowded.
And yet, it was perfectly normal for me to walk to school 40 or so years ago as a 6 years old, and it is now illegal for anyone under 9 to do so.
Yes. It's because the city I raised my kids in had cars speeding everywhere, including residential areas, running red lights and stop signs constantly and when a driver killed someone with their car, they were on the road the next day with no consequences.
Sure, it's multifaceted. But pedestrian fatalaties have gone down at least partially because children walk to school less often, in a reaction to the huge number of pedetrian killings of the past.
If we're using anecdotes, cars are the reason my kids don't walk independently, and the reason we're moving to the Netherlands next month. Drivers are the leading cause of dead children in the US.
Aside from directly killing children in impacts, car dependent design is usually hostile to walking anyway, for adults as well as kids. Walking to school is nice, but challenging when hundreds of parents late for work in tall, poor front visibility SUV's are running stop signs on the same streets where your child is walking.
