D.H.
The DS is definitely for older kids...my 8-10 year old nephews play with those. The controls are too small for my 4year olds hands.
We started with a V-smile...and he loves it..lots of levels and educational, colors, letters,etc.. The controls are bigger and easier for a 3-4 year old. My 5-6 year old nephews like it as well. We had trouble with one controller, replaced it and it works wonderful. It is two years old and the kids are not gentle.
We also have the Leapster and it is great too. The two products are very similar. The biggest issue we have is that it has a "pen" to draw with. My son sometimes has problems with it and gets frustrated. Many of the games we have need this "pen" to do at least some of the actions to move forward, even though it has one of those big knob controls as well. This is frustrating to my son and he will stop and switch to the V-Smile.
For the most part they are very similar and he enjoys both...my two year old enjoys wathcing...so for now, they are not fightingover it!!