Here are some good kids' websites that I know of:
clubpenguin.com
disneychannel.com
marapets.com
moshimonsters.com
Nickelodeon.com
pbskids.org
whyville.com
kids world
http://www.kiddieskingdom.info/
Webkinz and Poptropica are some good sites
some good kid web sites are... moviestarplanet.com animaljam.com and roblox.com
My fave website is fantage
Y8.com or y3.com or gamesbox.com and/or miniclip.com
Webkinz.com, babydow.com, pixiehollow.com, superpokepets.com, and howrse.com are all good Web sites for kids.
There's a heavily filtered roleplaying forum on moshimonsters.com. Some kids roleplay on sites like Animal Jam and Toontown, but they aren't as active. There's a good roleplay forum on kidzworld.com.
Try the automobile museum. There's usually some good stuff to look at there.
One can find a good review for kids online games on the games site themselves. Most online game websites for kids will have a section where you can read feedback about different games and sites. You can also use yahoo answers to look at some thoughts people have on different online kids games.
Here are some popular sites:NeopetsIcepetsPowerPetsWebkinzSee related links below.
nick.com is good club peguin rules moshimonsters cartoon network disney channel disneyxd and poptropica