> Growing up in suburban California I was basically in an outdoor prison until I could drive.

Just as a counter point, I grew up in suburban Massachusetts and this wasn't the case for me. My friends and I rode all over town on our bikes. Bike lanes weren't a thing back then at all, and this was in the 90s when violent crime was at its peak in the US. We just tried to stick to streets with less traffic, rode on sidewalks where available, and took alternate routes through the woods, the cemetery, private property, etc. to avoid busy areas. This is anecdotal, of course, but no kid from my town ever got hit by a car when I was growing up (one kid did die chasing a ball into the street, though).

I'm all for building bike lanes and public transport. And also not all suburban areas are equal - I've definitely seen areas of the US where I would not feel safe riding a bike even as an adult. But I think whatever is keeping kids confined to their homes is just as much a cultural change as it is a lack of infrastructure.