This game is a winning staple for any birthday bash--its rules are familiar, its action is quick and it adapts to just about any party theme.
One person plays Simon, and the others stand facing him. Simon instructs the others to perform an action by saying, "Simon says, do this," then demonstrates what is to be done. The other children must imitate Simon.
If Simon only says "Do this" while showing the action, the other players are not supposed to imitate their leader. Anyone who does so then steps out of the game. Players must also step out if they fail to imitate a certain action when they're supposed to.
Simon's strategy is to get the game moving so quickly that the players fail to notice when he just says "Do this" before demonstrating an action.