One of the reasons they live in such extended family groups is that a farm is a group effort. The kids are doing chores as soon as they can walk and comprehend simple commands. For a kid who is too small to help with the really heavy or skilled labor, driving the wagon somewhere for some supplies really quick might actually be a task he is assigned once in a while. And when the grown-ups are getting ready and loading heavy stuff into a wagon, sending the little kid underneath to check for damage might be a feasible idea.

Even aside from such situations, farming is a constant job that takes every bit of a farmer's attention he can give it. Any peripheral tasks that can be dumped on the kids, are so dumped.