Back in the days of family farming, everyone pitched in, and U.S. labor laws reflect this mostly bygone reality. This hasn’t been lost on commercial farmers, who use laws that allow children of any age at all to work on small farms and kids over 12 to work on a farm of any size. It’s a giant loophole you can drive a tractor through, and the tobacco industry is all over it. So is "The Daily Show," fortunately.
If you’d like to learn more about this, there’s a great article about kids and tobacco farming at Human Rights Watch.