When performing for children, one thing that really makes a difference to them is creating the illusion that they, not you, are responsible for the wonderous things which are happening.
Some might argue that you should do this all the time regardless of who your audience is. I'm not sure its always a good idea to give the audience credit fo what happens - but I do think its always a good idea to acknowledge the individual members of the audience and make them feel important.
This has turned into a bit of brainstorm but oh well. With regards to making people feel important, you can sometimes get a sense that a certain member of the group usually gets all the attention (maybe she has big boobs, maybe he's the jokester of the group, whater). Instead of making them feel important, focus on the people who don't usually get to feel important. The fat, flat-chested girl. The quiet guy who nervously laughs at everything the loud mouth says. You'll have much more of an impact on them if you make them feel special.