So Anthony Orsini, principal at Benjamin Franklin Middle School in Ridgewood, N.J., wants kids blocked from the sites at school and at home.
Orsini told "Good Morning America" today that the online taunting used to be limited to students in eighth grade or higher. Now he's seeing kids as young as fourth grade creating Facebook pages to bash a classmate.
"It's become meaner and meaner and they don't understand" the impact, he said. "They aren't socially and emotionally ready to understand."
He urged parents to make sure the computer is in a public space in the house and to keep an eye on their children's online habits.
"We see the times that things are posted on line -- 2:30 in the morning, 1:30 in the morning," he said. "Students are supposed to be asleep at that time."
"It is time for every single member of the B.F. community to take a stand!" Orsini urged parents this week via e-mail.
"There is absolutely, positively no reason for any middle school student to be a part of a social networking site!" Orsini wrote, calling on parents to prohibit their kids' access.
It's not so much the risk posed by adults that worries him, Orsini said. Rather, it's what children can do to one another in status updates, photo tags, and wall postings that's compelling him to act.
"It is not hyperbole for me to write that the pain caused by social networking sites is beyond significant," Orsini told parents.
Critics suggest it may be too late to bar school kids from social network.
Ellen Galinsky, the president of the Families and Work Institute, which researches changes in the workplace and in family life, said Orsini is "right on" in believing that children can do harm to each other on social networking sites, but she believes it's "folly" to think that young teens can or should be prohibited from accessing them.
"[Social networking sites] are part of kids' culture," Galinsky said. "We've just got to be very strong about using them well."
Facebook said its service is only designed for children ages 13 and over, and that young users have "on every page" the ability to report inappropriate content.
"I actually think the responsibility is not just a Facebook responsibility, it's a community responsibility," Facebook spokesman Elliot Schrage said Wednesday.
Still, Orsini told ABC News that he and his fellow administrators -- along with the school's guidance counselors -- spend "a huge amount of time" dealing with the social and emotional problems that arise online.
These issues have "totally taken over," Orsini told ABC News. "It's overwhelming."
Sixth, seventh and eighth graders famously have difficulty dealing with new friendships, budding relationships, bullying and the other interpersonal dynamics of the physical world.
"They simply aren't psychologically ready" to handle these issues in cyberspace, Orsini said.
"It is not worth the risk to your child to allow them the independence at this age to manage these sites on their own," Orsini wrote to parents, "not because they are not good kids or responsible, but because you cannot control the poor actions of anonymous others."