@neil There's so much to comment on here.
First: the main reason that parents give children smartphones, other than as a babysitting device, is to track them.
While the world is objectively safer than it was for previous generations, there's social pressure to know where your kids are at all times.
Up here, kids go to middle school (and therefore walk to school by themselves) aged nine.
Unsupervised use is another thing, but easy to see how it happens.