Children of any age are legally able to work on farms owned or operated by their parents, which would disagree with your premise. If parents are able to legally assume consent for their children to work on the farm, they would be able to consent for all employment opportunities.

For what it is worth, working on the farm as a youngster brings some of my fondest memories of childhood. I find it rather sad that people outside of the agriculture communities do not have similar opportunities until they grow older.