Hmm... people who can afford to send their children to school and can afford to keep them in school don't need laws to do that. And child labor laws do pretty much squat for low income children which drop out, get into gangs or find them selves on the street.

Laws only works when the society can enforce them and it doesn't mean police, social workers and the likes those are supposed to catch outliers not to enact reality. When society can't enforce laws/norms case and point children in low social economic environments laws break down and mean nothing.

Child labor laws might look like they prevent mass scale exploitation of children but in reality they don't, we stopped using child labor for the same reason we stopped using slave labor and it wasn't our morality but rather the simply practical truth that not only we afford to do so but they also in many cases are a liability.

The US industry has no child labor because it has not place for child labor, children can't be professionals most manufacturing is high end the physical labor is mostly automated and cheap "illegal" labor is available for the few tasks that children might still be able to fill (and if you really look into US textile sweatshops and the agriculture industry you'll still find child labor).

If the US had the same industrial landscape as the Congo or any other underdeveloped nation no matter what the so called moral compass of its population would point at, no matter if it would have democracy and all that it would have child labor that's just the reality we live in. We exploit every resource we have in the most efficient way possible, the locomotive and industrial revolutions made slave labor obsolete and the technological revolution made child labor obsolete both of those are fairly closely tied as when you need educated people not only to steer your economy but to drive it on every level they simply aren't compatible.