Don’t jump to conclusions. Children who work for pay usually make less than adults, but they are usually less productive too. It is far from obvious whether their employers take in more profits, or whether child labor undercuts jobs and wages for adults. You can speculate on this all you want, but now, for the first time, there is empirical evidence.
My study, “Child Labor Wages and Productivity” has just been published by the International Labor Organization (ILO). Working with teams in four countries, we surveyed children and their employers in two sectors per country, gathering data on the division of labor between adults and children, relative wages and productivity, firm-level factors, employer motivation, and the social context. You can read about children who fish off the coast of Ghana, repair cars and motor scooters in India and fold fireworks in the Philippines. The analysis is not particularly high-tech, but you can find basic wage regressions and estimates of production functions with child and adult labor inputs. There is also a ton of descriptive material.
The bottom line is, sometimes, under some conditions. When normal people talk about child labor they often assume that children are a gold mine for unscrupulous employers. This can be true, but it’s not the whole story. Meanwhile, when economists study child labor they usually assume the opposite, that the law of one price equalizes unit labor costs across all age levels. This is even less likely to be the case. If you care about child labor and want evidence instead of arbitrary assumptions, I think you’ll find the study up your alley.
It’s a free download at http://www.ilo.org/ipecinfo/product/viewProduct.do?productId=7065.