By Nora Young, CBC Radio - Spark

There's a lot of buzz in mainstream media about virtual worlds for adults, such as Second Life. But while socializing with an avatar is still a novelty for many North American adults, virtual worlds for kids and tweens are booming.

Sites with names like Stardoll, Habbo Hotel, Barbiegirls, Webkinz, Whyville, are popping up like mushrooms in Spring, appealing in particular to girls, who like the games and the social aspect of meeting their friends online.

Predictions are that more than half of online kids will be in virtual worlds within the next four years.

The business models for these worlds vary, from paid subscriptions, to direct product tie-ins, to third-parties marketing virtual versions of their products. If growing up with an avatar is going to be a natural part of young people's expression of their personalities, what role should advertising play in virtual worlds? Should they be clearly marked as separate from content?

Anastasia Goodstein is the author of Totally Wired: What Teens and Tweens are Really Doing Online, and she writes the ypulse.com blog. She'll be a guest on the next episode of CBC's Spark. She talks about how these virtual worlds for kids work, and whether young people can spot the difference between ads and content. You can hear the whole unedited interview here, or listen to it as part of Spark on CBC Radio One, on Wednesday October 31st at 11:30 a.m., and Saturday, November 3rd at 4:00 p.m.