I am not primarily a kid's show performer, but do have some experience in this field. Since some suggestions have been made as to good effects for kids, I would chime in with The Magic Coloring Book and The Egg Bag (proceeding with caution, as Reality One warns, not to make it a sucker effect, but rather, maybe let the kids "do the magic.")
I have also had great success with a version of the Professor's Nightmare by Trevor Lewis, he calls, "Stop, Look and Listen." It teaches kids safety in a highly entertaining and magical routine. The patter goes beautifully with the moves. Trevor understands young children, how they think, and how to entertain and engage them; he is a fabulous kid's show performer. I would recommend any DVD you can get your hands on featuring him if you want to learn from one of the best...