One of the most basic elements of music, rhythm is fun and easy to teach to children, and its also an essential part of their music education.
Try this circle game: The leader taps out a rhythm by clicking the claves or by tapping her shoe on the floor. The children, each with a pair of claves, are then challenged to tap out the rhythm played by the leader.
See Sarah's blog post "When Should My Child Begin Music Lessons?" for information on the benefits of teaching music to children.