The original story of that was a 12 year old being allowed to ride the New York subway by himself. https://en.m.wikipedia.org/wiki/Lenore_Skenazy

From your link, (1) it was a 9 year old, and (2) I don't see anything about CPS calls or any similar panic.

> Skenazy's April 1, 2008 column in The New York Sun, "Why I Let My 9-Year-Old Ride the Subway Alone," described her making the controversial decision to let her son take the New York City Subway home alone, which was completed without incident.

I recall my mother telling me that when I was 8, I used to take my 5 year-old-brother places — just the two of us — on the electric streetcar. I handled the money to pay our fares. This was in Milwaukee in the mid-50s. No big deal.