Current causes of global child labor are similar to causes in the past including poverty, limit access to education etc.
Families that were poor had to rely on child labor in order to improve their chances of basic necessities.
"Children had always worked, especially in farming. But factory work was hard. A child with a factory job might work 12 to 18 hours a day, 6 days a week, to earn a dollar. Many children began working before the age of 7, tending machines in spinning mills or hauling heavy loads. The factories were often damp, dark, and dirty. Some children worked underground, in coal mines. The working children had no time to play or go to school, and little time to rest. They often became ill."
Sources: "Child Labor." Reviewed by Milton Fried. The New Book of Knowledge. Grolier Online, 2014. Web. 26 June 2014. (use the date you accessed this page)