Fitness-Fatigue is not that hard of a concept.
hscoach: most of the problems “youngsters” have with this type of activity has to do with giving them the correct load. This really has to do with them having a lower maximum and tiring easier at higher intensities.
I have done this kids as young as 11 or 12 and never had a problem with eliciting the response I want. Instead of a jump or clean following a heavy squat or deadlift, the go from heavy medball (8-10 lbs) to using a 4 lb medball and a noticeable difference occurs to them.