I know a Tamiya lunchbox is really simple. My only concern with kits like it are that many of the screws are self tapping (into plastic parts) so it can require some strength.
But a kit like the lunchbox Im sure he will enjoy. There are still plenty of bits he can put together, even if you have to turn the screw driver for him.
Tamiya also has some really basic kits that are electric under their education series. These don't come radio controlled, but are small, snap fit+screw together and wont break the bank:
http://www.tamiyausa.com/items/geniu...-crawler-70211