National Geographic Kids

http://kids.nationalgeographic.com/

Ask Jeeves for Kids

http://www.askforkids.com/

Class Brain

http://www.classbrain.com/

National Wildlife

http://www.nwf.org/kids/

TimeMag for Kids

http://www.timeforkids.com/TFK/ 

FunBrain

http://www.funbrain.com/

Primary Games

http://www.primarygames.com/

Yucky Bug World

http://yucky.discovery.com/flash/