"Most sites for girls are an online world—it's socializing. For boys, it's gaming."
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For girls, "Broadly speaking, sites like Club Penguin allow kids to pick out an avatar that they guide through activities. As far as I could tell, this consists mostly of shopping and decorating. To purchase this fake clothing and furniture requires fake money, and to earn it, players are required to play a series of arcade-style games."
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For boys, "Ben went to his favorite site, Sports Illustrated for Kids. Through SIKids.com, he manages various fantasy teams and also plays online games. He showed Peter the site's All Star Dodgeball, where you get Shaquille O'Neal, Mia Hamm, and other athletes fight it out, if not to death then at least to unconsciousness. Then Ben went to AddictingGames.com and started playing Bowman, a game in which you control an archer and whose instructions read, "Your best shot is through the other guy's head."
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http://www.slate.com/id/2173912/