I highly recommend the late Shari Lewis'video of cool tricks and games for your target audience.
A favorite: Take two balloons, blown up. Stick a pin in one. It pops. Stick a pin in the other. Nothing happens. How come? Beforehand, take a small piece of scotch tape and stick it on the second balloon. Be sure to jab the pin in the spot covered by the tape. The balloon will remain intact.
My daughter amazed her thrird-grade classmates with this.