You've got your volunteer on stage, now what?
This is really important. When there is a volunteer with you, the show now becomes about them. You may want the show to be about you but what the audience is looking at is that child up there with you. They are expecting something to happen, they are expecting the child to do something, they know you wouldn't have asked for someone if you that person was just going to stand there...
There are lots of performers that ignore the child on stage with them. They use them as a table with moving parts.
You can have fun with your volunteer. You can tease them, whatever style of show you have BUT the audience is on their side. If the child asks a question, repeat it so everyone can hear. Give the power of focus to that child. You will double, triple quadruple your laughs.
All the addressing the audience, do it straight to that child. "I have an empty bag" Show the volunteer. The audience changes rolls, they are witnessing a secret, through the volunteer...one of them!
And here's a little secret (shhh. it took me a lot of years to figure this one out). After you say, "a big hand for susie" guide them to their seat. If the child goes on their own. continue the applause till they actually sit down. Do a "another hand for susie" if they are finding their seat or going to their mom.
When you have your volunteer, the audience, the parents on your side, everything you do will be funnier because everyone completely loves you, because you have given ultimate respect for the child (or children) on stage with you!