The Fair Labor Standards act, amended in 1996, has no stipulations for treatment of children over 16. 
Children 14-15 can do non-hazardous agricultural work after or before school. And children 12-13 can be employed with consent from parents or in the same location as parents place of employment. 
Healthier ways of getting your children interested in ag: 
4H Programs, Future Farmers of America, Sustainable Agriculture Resources and Programs for Children K-12