You can even print out a custom membership card. The National Institute of Environmental Health Sciences has a great collection of fun and educational online activities for kids. Even I had fun with some of these, being a big kid myself. Adventure, Inc. can be used for free. Printsville Kid's Clubhouse Hewlett Packard has lots of great projects kids can print and do.
Kids get a membership card and a quarterly newsletter.
PBS offers online coloring pages, storybook and various other activities. All kinds of fun safety related activities for kids including coloring pages and quizzes. ToyLab ToyLab has a nice variety of online games and activities for kids. Where's Waldo on the Web Surf the web to find Waldo and win daily prizes as well as a grand prize.