Less than a month after his sixth birthday, my son had to sign a contract.

He carefully wrote his name in block capitals at the bottom of a two-page document, agreeing to adhere to his Manhattan school’s guidelines on computer use. One of the most important rules was that he would not access social networking websites such as Club Penguin and Webkins, both aimed at young children. He and his fellow first-graders also agreed not to play games while connected to the internet at school.