You can make a rainbow–just follow the directions at http://www.tpwd.state.tx.us/publications/nonpwdpubs/young_naturalist/earth_sciences/rainbows/index.phtml . Then let your kids read the page and find the typos! Now your science project has turned into an English class!
And did you know there are lunar rainbows? The pic above is of a rainbow caused by moonlight–rather than sunlight.
Fun–and fun learning is forever learning.