Ten Fingers
This is an icebreaker game. Gather in a circle and put all ten fingers up. Go around saying things you've never done, such as "I've never ridden ridden in an airplane" or "I've never stolen something." If you have done the thing that the person says they've never done, you put a finger down. The last person with a finger up wins. This game is also sometimes called Never Have I Ever.
Magic Fabric
This is a warm-up game. You take a square cloth handkerchief or napkin, hold it up and explain that the children must use their imagination. Pass the fabric around the circle and each child must come up with a different thing the piece of cloth could be. Examples include, a cape, a flag, a magic carpet, a wrestling championship belt, etc.
Emotion Party
This improv game is a good exercise for getting kids to portray different emotions onstage. One person is the host and greets guests at the door as they enter the party. Each new person comes into the party exhibiting a different emotion. Everyone else who has already arrived at the party takes on the emotion of the guest entering the room. The emotion travels the room in a wave as each guest realizes the emotion in the room has changed and catches the new emotion.
Alphabet
Two people are chosen for the scene for this improv game and must go back and forth having a conversation, saying a sentence apiece. Each sentence must start with successive letters of the alphabet. To make it easier on younger children acting out the scene together, you might have an easel with each letter of the alphabet in a flip chart and flip it to the next letter as each letter is used.
Helping Hands
Two children act out a scene in this improv game with a third child standing behind one of them substituting their own hands for the actor's. It can get quite silly since the third child can't see what they're supposed to be doing with their hands and do things at odds with what is happening in the scene. It teaches the child who can't use their hands to think on their feet and the other child to come up with funny rationalizations for why the person's hands are not doing what they're supposed to.