Don’t worry about wheel size as it means naff-all, although I won’t say any more as it’ll start a forum riot ! But seriously, don’t be put off buying a bike just because it hasn’t got 650b or 29″ wheels. It’s much more important to worry about the paint job – honest 😉
That Voodoo looks really nice. It only lists a 16″ as the smallest size, so if that’s not too big it should give plenty of room to grow into.
I read once that Specialized are the most commonly stolen bikes, so perhaps a slightly more ‘unknown’ brand might be a good idea if he’s going to be locking it up anywhere. For the money, I doubt you’ll find anything better than that Voodoo.
Good luck.