There's yet another great yahoo group that I love called Click Schooling. They review lots of great online learning resources.
Diane runs the group and I am not allowed to share her whole review with you due to copy write laws, but here's the link from the Smithsonian regarding that famous George Washington painting you have seen your whole life, but probably know very little about
Smithsonian' s George Washington: The Portrait
There is a great section for kids with all kinds of learning tools.