buy the boy a neck brace support do-hicky and tell him no brace,no ride.
Them quads can really nail you when they bite back.
As for brands,probably stick with one of the Jap brands and if buying s/hand be aware that the independant rear ends have many parts to wear out(bushes,sleeves,cv joints,rubbers,uni's etc)
And pull the airbox lid off and check for an oiled filter,we see so many with a dry foam full of dust