Rich, for future reference...

Most kids, if they haven't been around 4-wheelers before, don't realize the importance of downshifting when needed.  I'd almost bet a dollar to a donut hole that a lack of downshifting is what has affected your clutch.

Try and show them the difference between how it takes off right away, from a stop -- in low, as compared to how it hesitates badly (slips clutch) when taking off from a stop, in a higher gear.  It'll only help you in the long run to give em a lesson now, otherwise as they get older/bigger, you'll be replacing burned up clutches everytime they want to go ridin'.