Supposing they do, why do you think they would use child labor?
Because they are bad parents who do not love their children?
Or could there be other reasons?
I would argue that legalizing and supporting child labor in industry helps mostly the companies which employ them, not the families who are employed:
It lets the companies get away with paying salaries to the adults which are not sufficient to feed a family. Indeed it
encourages paying such low salaries, because these force the parents to let their children work as well -- more labor force, at even lower cost.
If child labor is outlawed or boycotted, yes, maybe economic growth slows down somewhat. But industry margins would take a bigger hit than family incomes, I believe, since salary levels would have to increase somewhat.