I agree with your point that evolution of child labor practices was partly due to growing material wealth and partly due to cultural evolution, including norms influenced by legislation. Other people might give more credit to the laws. In any case you're more fun to talk to.

Legislation alone doesn't change the incentives of parents to try and do what's best for their family. And I don't think society had to be especially aware to recognize that sewing for ten hours until your fingers bleed is detrimental.

In 1850, parents chose between going hungry or putting 8-year-olds to work.

In 1980, parents chose between having a bored kid at home or encouraging him to earn pocket money.

Today, I pull my kid away from the computer to have him mow a corner of the yard with an electric mower, using safety glasses and noise cancelling headphones. It seems like progress, but I wonder if we have overshot some optimum.

I don't mean to compare my yard work to sweatshops, though I did sweat a lot. Like you, I enjoyed working. I don't know if child labor laws forbade my work, but if they had prevented me from working it would have been detrimental to my experience.