Have a look at the top 15 most popular kids websites in the U.S with Poptropica, Club Penguin and Moshi Monsters ranking high on the list.
1. Nick
2. PBS Kids
3. Nick Jr
4. Club Penguin
5. Cartoon Network
6. Yahoo! Kids
7. Poptropica
8. Moshi Monsters
9. Webkinz
10. Stardoll
11. Funbrain
12. Cool Math Games
13. Neopets
14. Primary Games
15. Fantage
Source: eBizMBA Rank (Alexa/Compete/Quantcast)