When I was in elementary school, there was a national anti-pollution campaign called "Give a Hoot - Don't Pollute!" and in Tennessee there was an anti-litter campaign called "Tennessee Trash" which ran a very funny PSA on TV showing a guy in an old convertible throwing out trash. The tag line for the Tennessee Trash PSA was "There ain't no lower class than Tennessee Trash." I think both were effective. But there is a difference between these anti-litter campaigns and today's anti-global warming campaigns. Give a Hoot and Tennessee Trash were aimed at encouraging people to act responsibly, not to encourage political activism.
Scholastic, the world's largest publisher of children's books, publishes a book that is used in many elementary schools today called Down to Earth Guide to Global Warming. According to this book, the first thing kids can do to help prevent global warming is to "Write a letter urging your mayor to sign the U.S. Mayors Climate Protection Agreement to reduce carbon emissions in your town."
If you are concerned that your child is getting only one side in school, there is a book out that claims (I have not read the book) to present an alternative to the current global warming orthodoxy, it is called The Sky's Not Falling!. The book is written by natural resources management expert Holly Fretwell and is for children 8 and up.
You may also want to visit the demand Debate website for a few other resources.