Some motions are beneficial in a song. Enough motion to keep the child's interest, but not so much that the total focus is on the difficult and hard to remember motions. This can then become a class in dance, not a kids worship time.
Although kids do love repetition, there should be some variety in the song choice. As the children grow older, they can accept a greater variety of songs. Sometimes three year olds can listen to the same song for hours. Also, try not to over tax the teachers and volunteers in your kids ministry.
GodsKidsWorship.com has a collection of Motion Songs by the Mighty Worship Motions band. These songs include a virtual worship leader who leads the children in the simple motions for each song. Because the leader is on the screen, with the words, no one gets lost.