Yes and no...My DS got the Leapster when he was 3. He could play it okay, but he needed a little more help (remembering which was the pause button, little things like that)...and he didn't play it that much. (He liked it fine, was just more into other things at that age.) He did, however, really love that letter factory video already mentioned, because it was more watching and not as much he had to do. Another one that he liked was the Cars game.
He's 4.5 now and LOVES his Leapster. So much so, that I've made a rule...It's only to be played in the car, unless it is too cold/wet to go outside and play, or if he is at home sick from school. Otherwise, he would do nothing else!