My nephews love the Wii. My brother and his wife also love the Wii because it keeps my nephews entertained and helps them to burn off some energy when the weather is nasty outside. Also, it tires them out before bed time.
This is why they are tired:
It is definitely better than them actually hitting one another and they do pretty well for a three-year-old (Brady on the right) and a nearly two-year-old (Max on the left). They also play tennis, though they can't really return a serve yet. I've seen them in action, and let me tell you, there is already a competitive nature bubbling to the surface of each of them.
Their parents will definitely have their hands full when the fight is over the car keys as opposed to which Wii game to play.