That case was an aberration. That's why it became such big news. If that were the norm, it would not have become national news.

This said, helicopter parents are real. I've ridden on amtrak many dozens of times, but never saw an unaccompanied child.

The only time I used Amtrak there was a child in the opposite seat. Staff put a sticker over his seat announcing that he was alone, which I thought was odd.

Meanwhile round here in London children get free bus travel, so it's very common to see them on local buses, and sometimes trains (tends to be wealthier kids on trains).

I've seen many on Caltrain in the mornings but many many more in Japan.