And even strict parents can’t always keep out the rest of the world. Kathryn Murray, a mother from the Upper East Side who asked to use her middle name instead of her first to protect her family’s privacy, said she limits pictures of her son to Picasa, a site that allows for invitation-only access. But she recently had an awkward moment when a friend told her she had posted pictures of her son on Facebook. She was considering how to ask her politely to take it down, when her friend, sensing the tension, beat her to it.

“My facial expression was enough,” she recalled.

Fueling the anxiety of parents like Ms. Murray is a doomsday scenario: a predator finds pictures of a cute child on the Internet, figures out where the child lives or goes to school and snatches him.

“It’s probably not too difficult to go through those pictures and figure out we live on the Upper East Side,” Ms. Murray said. “And then it’s ‘Oh, I’ve been to that park,’ or ‘I know that street,’ What’s to stop a pedophile from putting two and two together?”

Her fears are misplaced, experts on online safety say.

“Research shows that there is virtually no risk of pedophiles coming to get kids because they found them online,” said Stephen Balkam, chief executive of the Family Online Safety Institute. While the debate makes this crime seem common, he said, all the talk is really just “techno-panic.”

Prof. David Finkelhor, director of the Crimes Against Children Research Center at the University of New Hampshire, says TV shows like the “Dateline NBC” program “To Catch a Predator” have falsely inflated the danger of the Internet.

“There is this characterization of pedophiles using the Internet as an L. L. Bean catalog, but this is not the way it happens,” he said. Predators are much more likely to look in chat rooms or other sites, he said, where teenagers are suggesting that they may be open to a sexual relationship.