Was amblin' around in the U.S. Government Printing Office Online Bookstore (bookstore.gpo.gov) and found a great site for kids.  Informative, colorful, lively, educational, ta da, ta da, etc.  The GPO Bookstore isn't bad itself for adults.  Reasonably priced books and CDs on practically any topic you might want to know more about concerning this country, statistics on topics ad infinitum, procedures for dozens of methods, etc.

For the kids, check out http://bensguide.gpo.gov/index.html.  They use a cartoonized Benjamin Franklin (one of the early nation's most prolific producers of information, gadgets, gizmos, and ideas) as the "proprietor" of the site.  There are games for students about money and how it's made and its properties, games about history, etc.  Well worth your while to check it out!  I spent 1.5 hours "playing" when I should have been working!!  FUN!