If it's dragging and it's adjusted properly with enough free play then I think the friction plates are your best bet since I agree that it's highly unlikey he's beat the basket and hub too much so far. Unless your son is super aggressive I'm shocked he's trashed the plates in so little time, my kid beat on a KX80 for 2 seasons on the same set of clutch plates.
As far as the DP kit, you already own it so you may as well toss the plates in and give it a go, unless you are able to return it. We've tried kits from DP, Barnett, and EBC and I'll stick to OEM from here on out after my experience with those companies, others swear by Barnett kits so YMMV.