The corporations will prevent your law from existing or being enforced. Capitalists are not separate from the state, they are its primary controller.

If profits necessitate child labor then only a concerted anti-capitalist push will reverse it. Labor laws didn't emerge because they were good and popular they emerged because a militant labor force was already earning them through praxis and the state attempted to head off even greater gains through a legalized labor process that must follow "the rules", i.e. not use all of the tools at its disposal.

Basically by the time you'd get those laws and enforcement you'd already have the power to do even more.