Have your kids pant like a dog, hoot like a gorilla or meow like a cat -- but have them do in rhythm, on the same note. The point of these exercises, besides relaxing the kids, is to get them to use their throats, diaphragms and voices in ways they may not have before. Get them to feel their diaphragms move and their throats vibrate when they make sounds from deep in their chests instead of their mouths only.
Throw a bean bag back and forth around the circle. When you throw the bag high, they have to sing a high note. When you throw it low, they have to sing a low note. With very small children, bring a small stuffed or toy bird. Hold it high up in the air and sing the words “I am flying high” in a high pitch. Then hold it down low and sing “I am flying low.” Repeat this, getting them to sing with you. Then try for some middle pitches.
Humming is one of the simplest ways to warm up. Have your kids hum one note to begin with, then gradually move it higher. Have them pay attention to where the “buzzing” feeling is. A middle pitch will get their lips buzzing, a sensation they should enjoy. Then as they move lower in pitch, so the buzzing will move lower toward their chest. As they hum higher, the buzz will also move higher, up into their heads. This is because different cavities in the head resonates.
Scales are the bases for harmonies. Practice going up and down them with your students, but don’t press them to sing higher or lower than they are comfortably able to. Kids will love practicing the lip trill, which is when you relax your mouth and blow out so that your lips vibrate and make a "brbrbr" sound. It’s also called the bubble exercise because it’s the same thing you do when blowing bubbles under water. It helps relax your mouth and lips and improve breath control.