These days, it's little brother who's watching.

Younger and younger children want their share of the social networking craze, but popular Web sites such as MySpace and Facebook are reserved for older crowds. So sites are now aiming at children 14 and under, with online worlds where their animated personas can play games, chat with others their age and even engage in adultlike activities such as e-commerce.

This week, Disney announced the acquisition of Club Penguin, a virtual world for children that's been around less than two years but has grown to 12 million registered users, largely without marketing. Disney executives said the deal, valued at as much as $700 million depending on the company's performance, won't result in changes to the Club Penguin site, which requires parental permission for membership and doesn't have advertising.

But the deal has prompted child advocates to ask whether kids are helped or harmed by exposure to the Web.

"The perception in most of our minds is that Disney is wholesome and surely would not do anything to harm children," said Peggy Meszaros, director of the Center for Information Technology Impacts on Children, Youth and Families at Virginia Tech. "But it's dangerous to believe that any company in business to make money has the consumer interest at heart, whether it's a young child or adult."

There are a growing number of sites that claim to offer entertainment and education for children.

Disney said it wants to invest in sites where parents can be assured of their children's safety against adult content and contact from strangers, said Steve Wadsworth, president of Walt Disney Internet Group.

"It's a critical priority," he said. "This is one of the many types of entertainment that kids can and should be exposed to." Wadsworth said Disney does not plan to advertise on Club Penguin; the site sells premium memberships at $5.95 a month or $57.95 for a year.

Other sites targeted at kids, such as Whyville, make money primarily off corporate sponsorships for virtual product placement.

Whyville said its sponsored programs help kids learn about the real world, such as one funded by Toyota. There, children can buy virtual cars, make virtual monthly payments and review their virtual credit scores. If they fall behind on their payments, the car is virtually repossessed.

"Marketing done right involves real benefits to the kids," who learn about how the real world works, said James Bower, founder and chief executive of Whyville's parent company, Numedeon. "It's not parasitic, sugar-coated cereal advertising on television."

Some advocacy groups worry that Internet marketing could have a similar effect as television ads, which they say contribute to childhood-development problems, including obesity, youth violence, erosion of creativity and promotion of materialistic values.

"It teaches them impulsive buying and unthinking brand loyalty," said Susan Linn, a psychologist and co-founder of Campaign for a Commercial-Free Childhood. It is also more difficult for parents to monitor what their children do on the Internet than what they watch on TV, she said, and children engage with the products longer through the Internet than they would watching a television commercial.

Virginia Tech's Meszaros acknowledged that exposure to computer technology and the Internet can be important for a child's development, but so can other activities, such as reading, outdoor exercise and social interaction, she said.

"You don't want too much of any of those, but if parents aren't careful, kids will choose the things they love best," she said. "That may not always be what's best for them."