Let's be clear on a few things. First, there is a difference between child labor and child slavery. It doesn't seem to be the case above, but sometimes children want to work or have to work to supplement the family income. The children could also be in school. When I was in Guatemala, little boys would go around asking if people wanted shoe shines. However, they only did this on the weekend and were still in school. Child labor, yes. Child slavery, I don't think so unless they had some sort of manager forcing them to do it.
Second of all, let's be careful about what we define as child LABOR (I feel slavery is inherently bad) and if it's necessarily a bad thing. I think we have a tendency to think the world should follow our norms. In the U.S., one can work at age 16, but a 13 year-old would be considered child labor. Why do we draw the line here? We have our own cultural biases about what childhood actually is and when it ends. Some cultures would also contend that children working is an important part of growing into an adult and don't particularly care for us to force our values and biases onto them.
It's difficult to get people to see the cause and effect of their consumption. Most people need things (perceived or real needs), so they go to the store and buy them without thinking about the process by which the product was made. Though we can train our minds to think differently, I think our brains just function on a simple level because we dealth with very simple things for the majority of our species's existence.
I bought some organic, fair trade chocolate the other day (although, some investigations into "fair trade" have found less than ideal situations) . It was delicious. It as also $4.50 for a bar, but I don't need chocolate that often and when I do, I can at least support something that I find ethical. Perhaps the parents of these children will become wealthier as a result of me spending a little bit more and will have a choice for their children's future.