Did you know that originally laws required all coins to be made of gold, silver, or copper? You can learn lots about our money at the The U.S. Mint's Kids' Page. It is filled with games and teaching tools to help kids learn about money.
Some of the features that I enjoyed are the fun facts and information about circulating coins. You can learn the story behind each coin; a quarter did not have a denomination printed on it for the first 8 years it was made.
I'm always on the lookout for fun ways to teach kids about money. Check out the kids site at the U.S. Mint and let me know what you think!