I did a similar speech about 5 years ago in my college speech class.
Two things you want to stress are: SAFETY and SECURITY.
SAFETY: Despite the population increasing by roughly four times and gun ownership doubling, since 1930, the number of gun accidents have gone down over 80%. Check out the AR-15.com home page for the link to the story about CDC's new finding that children are having fewer gun accidents than ever in history. All of this took place before Brady, or any other type of Klinton gun legislation.
SECURITY:
Giving people the right to protect themselves reduces crime (See Gary Kleck's Books, and John Lott's book "More Guns, Less Crime.")
I'll email you, if you want, with some other good quotes from the founding fathers and other facts from reputable sources.
Good luck, and let me know how I can help. Also, explain how the NRA's Eddie Eagle program has helped kids learn about safety, and give out info on joining the NRA to your class!