Old enough to use technology well, but young enough to require oversight of some manner.
Americans seem to have a very strange notion of what children can do at what ages. Kids at age 8 can reasonably go to and from school if it's close enough. This of course relies on living in a walkable area and I guess that's partially where the problem starts in the US. Parents got used to the idea that kids need to be transported by car or a specific, restricted-use school bus, leaving no freedom or agency for the children. Yes, growing up involves making mistakes, doing mischief, testing boundaries, learning what it is like to lie, feeling what a resulting bad conscience feels like, what a secret feels like etc. Yes, it may mean that the kid may skip a class or go somewhere they are not supposed to, but usually these aren't life shaking mistakes, unless there are deeper problems at home and with the parental environment.
However, a truly dictatorial parental surveillance scheme, as is now possible through tech, may inhibit the information transfer even more. Combined with practices like constant parental transportation, structured extracurriculars every day, no recess at school or homeschooling a very dystopian picture emerges.
I really hope this wave won't hit Europe.
And the effects are already showing: https://www.economist.com/graphic-detail/2019/02/27/generati...
Mother who gained custody had sever bipolar which led to days where she literally would not get out of bed.
When I was in 6th grade I remember having to pack lunches for my sister who was 4 years younger and make sure we both went to the bus stop and got to school each day.
It was a bit more difficult when I hit the 7th and 8th grades as the school in the area started those grades an hour earlier than K-6 and my sister and I no longer rode the same bus at the same time.
We managed pretty good, and my sister and I are very close to this day because of how we took care of each other growing up.
I also had immense freedom, no curfew/bedtime and freedom to roam unsupervised unless my grades slipped. I enjoyed the freedom so I managed to keep my grades up my entire education.
It helped that cell phones in the hands of every child were still not a thing, just as I turned 18 and moved out on my own is when I remember getting my first cell phone.
Again that is cherry-picking.
Yes, I walked to school alone when I was 12. Also when I was 7.
But school is a consistent, well-known location with adult supervision at the destination. The amount of maturity required for traveling to school is minimal.
Kids can do a lot more open-ended activities than walking/taking the bus to school.