They would be helped by better job opportunities where they live, by more governmental protections for workers where they live etc.
But, someone buying stuff made by their employer is not what harms them.
It is exactly what harms them.
With that logic one can defend keeping children in tantalum mines in the supply chain of an iPhone. That's not an acceptable status quo...
Removing the market for immoral exploitation of beings and the environment is a necessary step. The size of the market for things made fairly needs to grow.
As a consumer one of the few immediate means of action we have is to at least refuse these products when we can... Then yeah, vote, donate, get involved for these kids to live decently.
I kind of understand why China invests in Africa the way it does vs how the west seems to just throw charity and morality at it. Development would solve the problem naturally (a richer society will stop sending their kids to the mines, or having their schools organize them to make fireworks, a sad state of affairs that happened less than two decades ago in China but now is unthinkable).