Club Penguin was started more than a year ago as "an online playground for kids," said Lane Merrifield, the site's co-founder and chief executive. "How can we take the fun pieces of these more grown-up and adult (social-networking) sites and surround them in a safe environment?"

Kids win gold coins by playing games such as sled racing and, with a paid membership, buy virtual items like furniture and clothing. Kids can attend parties and make friends by adding other penguins to their buddy lists.

The site, from Canada's New Horizon Interactive Ltd., does not try to keep out older users — after all, anyone can lie about age. Rather, it builds in controls meant to curb outside contact and harassment. The company says it has never had a problem with predators.

Parents can choose an "ultimate safe" mode, meaning chat messages sent and received are limited to prewritten phrases, such as "How are you today?"

In the standard mode, kids can type messages like any other chat program, but only the sender sees messages containing foul language and even innocent-sounding words such as "mom" — to prevent someone from asking, "Is your mom home?" Senders would think they are being ignored and not try tricks to bypass filters.

The filters also catch numbers that might form a phone number a kid is trying to share, even if someone tries to replace "1" with "one."

Veterans can apply to become "secret agents," responsible for patrolling the site and reporting bad behavior, and violations can get a kid banned for a day or longer.

Likewise, Webkinz limits chats by permitting only prewritten phrases, and e-cards go only to those already on friends lists.

Kids take quizzes or perform chores to earn "KinzCash" to buy furniture for their virtual room and food for their virtual pet. They must return to the site regularly to keep their pets fed and healthy; otherwise, it's a trip to Dr. Quack for medical care, though the pets themselves never die.

Unlike Club Penguin, though, access to the Canadian-based site from Ganz is restricted to those who buy a Webkinz plush toy at a retail store for about $15, many of which have been selling out because of high demand. Think Beanie Babies with an online component. A code on each toy unlocks the site for a year.

Both sites do require some reading skills, though younger kids can participate with older siblings or parents.