Reddit reviews Creating 3-D Animation : The Aardman Book of Filmmaking

This software is very nice and what many professionals use ( https://www.dragonframe.com/store/products ). It allows you to use an external controller, as well as having many features which make animation easier.

That said, there are many free or cheaper programs that would do the trick too. If he is serious about animation, I would recommend Dragonframe, but if it is a passing fad, perhaps not worth investing that much.

Also, do you know what camera he is using? If he doesn't already have one, a good DSLR with liveview will enable him to use the onion skinning features on a computer, as well as produce superb images.

Lighting is another aspect that needs some gear, perhaps some small film lights to help him.

If you can't decide on gear, there are TONS of awesome books that will help foster his creative spirit. I bought this when I was younger and have loved it ( http://www.amazon.com/Creating-3-D-Animation-Aardman-Filmmaking/dp/B000C4SYGQ/ref=sr_1_1?ie=UTF8&qid=1322423038&sr=8-1 ). Also general books on lighting and film techniques apply to stop-motion as well. There are tons of other books as well: http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Dstripbooks&field-keywords=stop+motion&x=0&y=0

Another fun idea would be a subscription to Stop Motion Magazine: http://stopmotionmagazine.com/ Their site seems to be down at the moment, but it is a great little magazine.

I think the best thing at his age, and what I wish I had had, would be access to more information and knowledge. Books, DVDs, stop-motion movies to learn from, etc. Gear is great, but half the fun at his age is trying to figure out how to overcome your lack of equipment in a clever way....

Does he have links to any videos online? If you could find out what camera/software he is using, perhaps I could give more specific advice.

Hope this helps!