Sounds like a great time! Here are a few hints that I can think of:
You probably already know this, but keep in mind that people have three major learning styles - tactile/physical, visual, and auditory.
If you use pictures or video, try to include some of a kid or kids of about the same age or a bit older. This will help the audience relate.
Depending on how much time you have, you might want to get the class to build a paper airplane. Here's an example (click on the image for more details):
Be sure to bring some good paper for all the kids!
You might want to see if someone like Sporty's would donate some of those very small, thin logbooks, and give one to each kid.
Have fun!