check RCKens thread at the top of the beginners forum,there is a bunch of trainers to look at there all pretty good,then go to http://www.modelaircraft.org/ the AMA site where you can join the membership provides insurance as well as a magazine.

most clubs require some sort of insurance and depending on your sons age his membership should be fairly inexpensive,the AMA also has a club locator, to find one in your area.
before you purchase a trainer check out the local club and see what they are using radio brand and the availability of instruction some clubs have formal rules for instructors some are more flexable you just show up and someone who is willing helps out,best to check out as many as you can to see which one fits your style and what you want to pursue such as scale warbirds,pattern flying,competition or just lesurly putting around the sky whatever interests you and your son.

something to invest in as well would be a simulator for the computer, its a invaluable training aid there are several, the one I have is the realflight G-3.5 there's now a G-4 which is the newest version of that brand.