Depends. Children learning a trade from their parents and family friends is probably a good thing.

Children going to work for GloboHomo and learning the exact same evil value system as they'd learn in school is definitely a bad thing.

If child labor is legalized, which of those two things is more likely to increase? My guess is the latter, because the people doing the former are probably already doing so with little regard to child labor laws. If Libertarians think by repealing this law the days of apprenticing at Mr. Fezziwig's will return, that's unlikely.

More likely outcome: children will now work for GloboHomo and be paid to attend the mandatory Diversity, Equity, and Inclusion classes they used to take in school.