I found this site mentioned on Technology Tidbits: Thoughts of a Cyber Hero
Chess Kid is a great site to help kids learn how to play chess. It contains simply-explained rules of the game, video and text explanations of various strategies, etc. It is also a great resource for teachers, parents, or coaches who would like to incorporate these skills into a Chess club, Weekly Advisory activity, etc. Kids can sign up for a free account to learn the game or track their progress, or they can skip the sign-up process and still access most of the benefits of the site, which appears to be completely free to use.