It is true that the kids in my suburbs never go outside - that’s because people have retreated to their backyards and built wonderful play areas and swimming pools for the kids and grandkids - behind high fences. Much safer that way.
That said, an ice cream truck heads through our area once a day during the summer playing Christmas music. One often comes later, after dinner - that one plays The Chicken Song.
I keep hearing that as a reason suburban kids don't leave their yards but I've been walking those neighborhoods for decades now and have never seen anything or anybody that could be construed as dangerous to children.
I grew up in a bit of an urban jungle yet was outdoors pretty much every daylight hour during the summer, riding my bike, playing pickup ball, and just generally hanging out with my peers with no parents around and getting into the typical juvenile (minor) mischief. And yes, I did get picked on or even beat up from time to time from the bigger kids.
I don't thinking walling children off in their backyards is very healthy. When they grow up, they tend to be super-sensitive, easily rattled and in the case of boys, very weak and effeminate (at least by the standards in which I grew up back in the 1970s).
During the school year, as I take my walk around the neighborhood, I see most parents driving their kids to the bus stop - sometimes even to the end of their driveways. The kid doesn't leave the car until the school bus is stopped. Then when the school bus returns, the parents are right back there waiting for the bus to pick them up. I'm not talking first graders either. These are kids probably in sixth or seventh grade.