Poor judgment... yes. Unfair to his kid and the other adults present... yes. Maybe he deserved to be pulled from the race. But arrested for this? Absolutely not.
1980s: I was a latchkey kid starting in the spring of 2nd grade (age 8). I took the city bus if I missed the school bus starting in about 4th grade. My friends and I would bike several miles to a city swimming pool, check in, and go swimming. No adults required. Went to the library solo or with other kids, no adults. We also did stuff like knocking on strangers' doors and shoveling snow for money. By 6th grade we had moved to a big city and I took the city bus (complete with homeless people) daily home from school, including a transfer. We would collect cans (yes from garbage cans/dumpsters) for money and even worked at a local business, sweeping and vacuuming for $1 per hour (no joke) at age 10-11. Then we would spend it all at 7-11 buying candy, Garbage Pail kids, etc. So yes, I'm a free range kid.