Blame city planners in the pockets of developers who in a way are doing what taxpayers want.........cheaper everything.
You wind up with cookie cutter neighborhoods with houses 3' apart and people having to street park due to short driveways and tiny garages that won't fit a Prius.
Then these packed neighborhoods are obviously busier, even ignoring that they are isolated from any trail or pedestrian/bike infrastructure.
I live in an older neighborhood, when people had some damn sense. We have lots of kids up and down the streets all the time.
People are so desperate in the US for their 1500 sqft house on 1/8th acre with a mule that they don't even bother to think how crappy of a deal they are getting. And how crappy that kind of development makes car traffic all over town.
But.....................all of that is a red herring...............it's actually all about parents being a bunch of lazy morons and allow kids to stare at a screen everywhere they go. On the way to dinner, at dinner, on the way home from dinner, once they get home, etc......... Screen zombies.
Solve that, you solve the bike and kids thing we're talking about.
You don't even get to the safety argument without addressing the crappy parenting part.
And I'm sorry, it is crappy parenting to pacify a child for their entire life to the tune of hours per day with a screen/device.
You seriously trust the freaking internet and entertainment industry to raise your child?