From the Webkinz site
Webkinz pets are lovable plush pets that each come with a unique Secret Code. With it, you enter Webkinz World where you care for your virtual pet, answer trivia, earn KinzCash, and play the best kids games on the net!The 'lovable plush pets' are $2 stuffed animals that sell, when you can find them, for over $10.
The animals are quickly forgotten - it's the 'Secret Codes' that the kids want. Without the code that comes with the pet you can't enter the fun exciting virtual world. Consequently, kids place great value in the codes. Search on the Web and you'll see a whole marketplace for them.
That explains why, when my 7-yr old son was playing at a friend's house the other day, and they were logging into the Webkinz site, my boy left the room when his friend entered the code (as reported to me by the Dad). I asked my son about it before he went to school today. I asked him if he left the room because he wanted to, or because his friend has asked him to. His reply
I wanted to, I never want to know somebody's else code in case something goes wrong and they might think I did it.
Smart boy. I'm all verklempt from pride.