Vigilant parents and well-educated children remain the first line of defense against online predators, even as social networking sites toughen standards and police crack down, experts told a panel of governors Sunday.

Law-enforcement agencies are becoming more technologically proficient in the fight against cyberspace child stalkers, New Hampshire Attorney General Kelly Ayotte said. But they alone can’t solve a problem so widespread that one in five kids who use the Internet are believed to have been approached by a predator, she said.