Used this with lots of students aged 6-9. They all love it. A very safe way to introduce social networking and virtual worlds to young children. Builds on Kid Pix skills and includes simple games. Experience grows as use leads to more features (tools, books, games) emerging. Students continue to send me animals and messages over the summer.
Wow! LOVE this site. My 5 year old daughters discovered this recently and now we battle for our own computer time. They love drawing their own creatures and delight when they come to life! What's great is that the more they play, the more games they enjoy, the more design tools are added. I am dumfounded at the rate at which they've picked it all up and watching them enjoy it so much is such a pleasure!
This has been one of my son's favorite sites since he was three. Although he started using it at three, it took him a while to figure out how to use the games, and I was explaining and demonstrating a lot to him to compensate. I think it's more age appropriate for 5+.
With that aside, I love the creativity it brings out, as members get to draw their own pets, pet food, cars (to play games in), and even the background for the world their pets live in. Once drawn, the pets become animated (okay, they really just wiggle around, but it's cool), and are fun to interact with. You can also create multiple worlds, or unlock new drawing colors/patterns/brushes by playing the games and winning.
Negatives are that some of the best features can only be unlocked with a paid membership, so if you don't feel like paying $5.95/month, then you won't have all the features.