I 2nd the Super Cub LP BNF. Easy to fly, easy to fix.

Put your son on a sim first. Buy Real Flight 5.5, its a little pricey, buy after you and your son are flying RC and have mastered the sim, you can sell it here or RCGroups or ebay. You will get most of your money back at it will save you money in non-crashed RC planes.

The sim does not replace joining a club and learning from the guys there. It will give you both a lot of stick time at home to get your thumbs up to speed.