Best gaming system for kids: PS3, wii, or xbox?

I don't have a wii, but for kids that age I'd say it's the best. I have a 4 year old daughter and I've had both an XBox and PS3. She can't really do much with either one. I have a Spyro game and some racing games that she plays with sometimes, but all of the buttons are just too difficult for hear to reach. I'd say between the easier controls and more kid friendly content, the wii is the way to go.