All of which is irrelevant to the fact that the best option for many children (again, revealed preference) is to work, and depriving them of that option is like

All of which is irrelevant to the fact that the best option for many children (again, revealed preference) is to work, and depriving them of that option is likely to lead to a net worse condition. But to your point, I'm quite certain that "China" would prefer to have an economy sufficiently productive and wealthy that child labor is no longer a choice parents feel they need to make. Banning the effect does not change the cause.