Getting children in touch with the rhythms in music is a great way to help them warm up. You can play a musical selection with an easily distinguishable beat and ask them to clap on the downbeat or on all the beats they can identify. This instruction may result in some cacophony, but it will help children begin to experience the music not only with their ears but with their bodies. This can help them connect with music in preparation for further instruction or musical activity.
Having children hum can be an excellent preparation for singing or listening activities. Not only does it allow them to create sound with their voices, the vibration in the body brought about by humming helps prepare them to further engage with music. You can lead children in humming activities by singing a tune and having them hum the melody. You can also play a piece of music, with or without words, and ask them to hum along with the piece. Humming also helps prepare the body for singing, as it involves the flow of air from the lungs, over the vocal cords and into the mouth.
Circle games allow children to not only connect with the music but with each other. If they are getting ready to play or sing music together, circle games are an excellent starter activity. You can play a sort of "follow-the-leader" game. Ask the first child to make a sound or a simple movement and then "send" that sound or movement around the circle, as each child recreates the sound for himself. By the time the sound or movement comes back to the originator, ask the class if it has changed. Children usually enjoy this game because it allows them to participate without feeling uncomfortably singled out. Chances are, everyone stands a chance of looking a little silly. Another game to try is to have one student pronounce the first word of a song, the next student continues with the second word and so on until the lyric is complete. Again, this game lets students participate within the safe structure of the group.