Some fun and useful websites for kids:

 Reference site with homework help. This site allows students to make their own secret messages and learn about cryptography. 

Funbrain Lots of games and resources. 

Primary Games Educational games. 

Online Activities Online drill activities for math and language that score your results! 

The Diary Project Students record their experiences in journals and talk with kids worldwide. A great interactive site with animated movies. A large search site for homework information.