If he can drive the software to upload programs to the Arduino something like the SparkFun Inventors Kit or Mini Inventors Kit might be a good idea. It comes with a breadboard, sensor, buttons, a servo, wires etc. It would be something he could build on (harder to do that with the snap together kits).
If you want to participate, it would also be cool if you got the same kit and you could go through the projects together and compare notes on Skype, Hangouts etc.
-grantbob