In my experience with community demonstrations, our most common questions tend to be along the lines of "How did you manage that?". As suggested above, at elementary and middle school demonstrations, we give a brief overview of the team, [tangent] much like the cute little presentations that colleges usually have in regard to their undergraduate admissions [/tangent], followed by allowing students to drive one at a time, while the others ask questions. At larger events, we simple scale this up (Much thanks to all the teams that come out to lend us a hand, erm, robot, each year at the NBC tech expo).
A brief presentation can do away with what some call "pointless questions". Practice, practice, and 9 out of 10 opinionated people agree that elementary students are a prime practice ground for public speaking skills. They're very forgiving.

On a side note to an already growing response, we did have one elementary school student ask us one time a set of questions that was along the lines of, "What is the gear ratio of your drive train?", "Is it possible to do trig with the processor you have, or do you use something else to approximate it in your autonomous?". The moral, be prepared to answer any question.
For more information on how we set-up our community outreach programs, including demonstrations, visit our website, or give me a PM.
[plug] Miss Daisy's "Team in a Box" DVD and CD set has a section on giving community demonstrations. You can request a copy by also visiting our website [/plug]