My four year old loves playing Tic-Tac-Toe.
He doesn't understand some of the nuances and "plays" that you can pull off to set yourself up, but he gets the concept and enjoys winning more than losing.
The other night at the Pacers game they played a halftime game where the participants had to hit a layup and then they got a game piece, first one to get three in a row and complete a tic-tac-toe wins.
Watch these two dummies prove to the world that they don't really know how to play a child's game.