I think 5 is much too young. Our 7yr old has a DS, and he got it last year for Christmas. He was 6.5 then, and looking back he was much too young for it. We put a very strict time limit on it, 1/2hr per day after homework and before dinner, that was it. HE still has that strict time limit, and he does fine with it. He could read by age 4 so he had no problem playing the games, and he enjoys the board games on it, like Risk, Clue, Moustrap, etc. He also has a couple Mario games, and a couple racing games like Matchbox racing, Four wheeler/hot rod racing, Mario Cart, Cars racing.
The system itself is not meant for little hands. Wehave a case on his and the hinges still broke after 3mos with minimal careful use (remember he only uses it 30mins a day if that) Its delicate and not one of the games are educational, and IMO there are much better ways for a 5yr old ot entertain himself.
And I certainly would NOT allow him to take it on the school bus, I'd guarantee you would be out $150 the first day or two he brought it, because it would be stolen, broken, or lost. A 5yr old doesn't have the maturity to bring something like that to school with him. Plus the games are the size of a memory card, very small and easily lost.