Contact your FIRST Senior Mentor he should have some of the promo DVDs.
"Student Voices"
https://www.youtube.com/watch?v=V6hq2qFqCAM is a quick overview of what FRC is about.
Or the longer version "What's FIRST?"
https://www.youtube.com/watch?v=u7k5IxsixO4
What's FRC
https://www.youtube.com/watch?v=b3_6...5f3yeYxEADZuvQ has a good overview of all the aspects of FRC.
However for your type of target audience the classic Morgan Freeman is my go to video.
https://www.youtube.com/watch?v=i1QyM9WTF18