I agree, it doesn't seem that extreme to me. Maybe something like letting your 9 year old get on a bus to another state, without a phone, and telling them "come back when you're done having fun!" would be extreme.

My grandfather did this with my father - though with specific marching orders. Regularly, maybe starting when dad was 7. It was the 1920's (s/bus/train/g). So far as I can tell from old family stories, it was considered pretty normal for an extended family with farms that were hundreds of miles apart. When school was out, the "free" young farm labor could be sent to where there was work that needed doing.

We stick kids on the plane unaccompanied to be minded by a flight attendant.

That may be because myself and many others here live in areas where we never rode trains or subways at all.

Riding the subway is far safer than being driven in a car.

https://usa.streetsblog.org/2014/12/19/heres-how-much-safer-...

Well the fear of letting a child go by themselves would be that they would get lost, kidnapped, or robbed.

The fear may be real, but the risk isn't.