yo ella
I agree with you, the older console systems beat the new games by afar!
As said before, be sure which DS the kid wants exactly (one of the original DS(like DS Lite, DSi, DSXL), or the new DS3). The DS3 is cool because the graphics are 3D! Most newer games will only function on the DS3, for that. The Wii is definitely a good choice and very child-friendly(and also cool for older people), like all the Nintendo products. There are also a lot of ports of old games for the Nintendo consoles.
I have the original, old DS, and I bought a flashcard called the R4 that let's me download the games from sites that rip the games for free. You might want to look into those, because they saved me a lot of money
I don't have much time for playing on it because of school and everything though

I have to say, though, that the future of portable gaming lies more in the smartphone products. It might be even a better choice to buy him an iPod Touch! There are great games in form of apps these days.
You can check out this link to find the best rated games for the DS/DSi:
http://ds.ign.com/index/reviews.htmlMost of the best games for the consoles are made from Nintendo themselves!
And here's a personal favorite of mine:
http://www.youtube.com/watch?v=m0k7vsy4j_w