According to a couple news stories I’ve seen pop up from time to time, we have child labor in the US too. It’s not legal and the children are usually the children of illegal immigrants. Maybe it’s sort of the same deal over there i.e. desperate people doing desperate things despite the norm.
Now that you mention it, I was a soccer ref when I was 15. You’re right, it probably varies by state. I guess “child labor” is a pretty broad term that could include delivering newspapers and processing chicken on a factory floor.