Unless you plan to lock them in a room without Internet, you can't. It is really up to the parents to decide. For example, I let my daughters have one when they were 13, but I had their password and had to be friends with their friends. If I saw anything inappropriate, I was able to step in immediately. Also, I put parental controls on the computer that notify me if a second account is created and will even log chats and posts if I want. One daughter did try to make a fake account and I caught her at it and we went unplugged for two weeks as punishment (no cell phone, no computer, no iPod). However, you can't control what parents do with their own children and many are not on top of things these days.