Contact Hetrick Racing for all your mini quad needs.
I have the same machine. I'd start out with their power up c-kit for $340 and go from there. Maybe add a clamp-on Uni filter and outerwear for another $30, and see how he likes it.
http://www.hetrickracing.com/youthqu...owerupkits.htm
After that, I'd suggest a bigger carb and some port work.