The American Library Association has updated their site "Great Websites for Kids" since I looked at it awhile ago. There is a wealth of information here and its easy to use. You can look under subject tabs such as history and biography, science, mathematics, arts, etc. Or, you can check out the sites by most popular, site of the week, or top rated.Great Websites for Kids is a compilation of exemplary websites geared to children from birth to age 14. Suggested sites are evaluated by the Great Websites for Kids Committee using established selection criteria. The committee is made up of members of the Association for Library Service to Children, a division of the American Library Association.
Newly evaluated and accepted sites are added to the database three times a year. The committee also reviews all sites within the database twice a year to guarantee sites are still relevant, appropriate and accessible. You can also suggest websites for their consideration.
Find the site at http://gws.ala.org/