Hi D. - I have an almost 3 year old daughter who simply loves playing Wii. In fact, although we bought it for my son who was 9 when we got it, she plays it more than anyone in the house.
She does the Wii Fit (yoga, running, step, balance games, etc...and although she loves the Hula Hoop, she needs help with that because the board doesn't register her tiny hip movements!), the Wii Sport package (tennis, baseball, boxing) and Mario Kart racing.
She's independent to the extreme and really likes the whole process, starting with loading the games herself, getting herself started and navigating the screens.
I have a very energetic child, who much prefers the great outdoors, but Wii has provided a great way to keep her active on these frigid, stay-in-the-house days.