The problem with rampant capitalism is that eventually you run out of other people's children to send down the coal mines.
It's not a problem really all that happens is that the cost of labour increases increasing the cost of your final product. If people agree that we shouldn't have child labour and can afford to pay more for products they will. That is the real beauty of true capitalism is that it is self correcting. If something becomes too expensive to produce the market will soon figure it out and people stop buying the product or change their spending habits.