Everything I did as a kid was more dangerous because I was an uncoordinated idiot with no sense of danger. I'm still mostly better off for having done the stupid things I did.
Why does attaching pay make it special?
The only aside is that I don't want to end up in a world where substantial fractions of children must work in order to be fed and housed. But if a kid wants to work and someone wants to pay them to, it seems good to me.
Incentives. A bouldering gym is incentivized, due to the cost of liability and the impact on their reputation, for every visitor to have a safe experience. If your kid falls and breaks his neck after you paid a gym to help him learn, you’re going to sue.
Employers are incentivized to extract as much labor for the least amount of expense. New laws disincentivize safety by reducing liability.
I benefitted tremendously from work I did as a teenager (but did not have to do to survive). Obviously there's some bathwater and some baby here and it's a difficult balance, but I think completely banning the practice is unlikely to be the best possible outcome.