Teens: It's a diary. Adults: It's unsafe.

Earlier this year, 13-year-old Shannon Sullivan of Wood-Ridge, N.J., was socializing in the same way as dozens of her classmates at Our Lady of the Assumption School. She maintained a personalized page on a website that contained her photograph and details about what makes her unique. Friends would surf by and leave fun messages.

But then her mother found out. And now her site, and those of her friends - once lovingly adorned with everything from sound bites to video clips - are fast disappearing at the insistence of their safety-minded parents.

"They're not aware how easily something [predatory] can happen over the Internet," says Shannon's mother, Margaret, who is a computer-science teacher at Assumption. "They really shouldn't have these sites. Maybe when they're older, in college or something, but it's just not safe before that."

In taking on the Web-posting habits of their children, parents are picking what can be a thorny fight. Personal Web pages for the preadolescent and teenage set seem to have become as common as diaries and locker decorations once were.

Of the world's approximately 38 million "blogs," or self-published Web pages, 52.8 percent belong to those age 19 or younger, according to survey data from the Perseus Co., a maker of Web-surveying software. By year's end, the firm expects the total number of blogs on the Web to reach 53.4 million.

Meanwhile, Perseus says the typical blogger continues to be a teenage girl who uses the medium primarily to communicate with five to 10 friends.

As technology-savvy youths enlist computers in the timeless teen quest to establish identity, some adults feel the stakes are too high to accept it as just another form or phase of self-expression. In this camp, crime worries trump a desire to honor young people's privacy.

Internet stalkers have killed at least four minors in the past three years, and law enforcement authorities count about 5,000 reports of attempted sexual predation over the Internet in the past year, according to Parry Aftab, executive director of Wiredsafety.org, an Internet safety organization.

Given such statistics, parents need to get over the feeling that they're invading their children's privacy by reading their blogs, Ms. Aftabsays. She believes that parents must bring their judgment to bear on the content of what's posted. "When you get hormones pumping, [minors] are operating the heavy machinery of the Internet under impaired judgment."

Others fear, however, that certain precautions could amount to swatting a fly with a sledgehammer, and could take a hefty toll on family life. The likelihood of tragedy is far greater whenever a child rides in a car or goes swimming than when he or she posts his or her name, photograph, and other personal information on the Internet, says Laurence Steinberg, an expert in adolescent psychology at Temple University and author of "The 10 Basic Principles of Good Parenting."

After age 13 or 14, he says, children with a good record of being responsible should be able to post personal content without parents looking over their shoulders.

"The downside of prohibiting it is worse than the downside of allowing it," Dr. Steinberg says. "A good parent-child relationship is based on trust, and trust is a reciprocal feeling. I think people do get especially worked up for some reason over the Internet. But snooping on what your child does on the Internet, to me in some ways, is no different from snooping through your child's dresser drawers or eavesdropping on your child's telephone conversation or reading your child's diary.

"Any of those things done without cause [for suspicion] are to me violations of what I think is the reasonable right that teenagers have, which is to have some aspect of their lives that their parents are not privy to," he says.

Though the value of pursuing a reasonable level of safety goes undisputed in this discussion, adults differ on the value of increasing a child's freedom and privacy over time, especially in cyberspace.

Aftab of WiredSafety.org supports adolescent privacy with pen-and-paper diaries, for instance, because the content there is "between [the child] and the page," whereas website content is "for the whole world to see." Posting private Web content before age 16 only invites trouble, she says, yet many teens do it in a highly public bid for "attention, recognition, and affection."

Lisa O'Beirne, another Assumption School mother of a 13-year-old, tries to put safety first. For example, she got her daughter a cellular phone, she says, "so I always know where she is." She calls her daughter at least once every 30 minutes whenever she's not in school. She says her daughter, Ashley, at first protested, saying, "Why are you always calling me? You're embarrassing me." But in this, as in her rule forbidding Web postings by her daughter, the rationale is that the end justifies the means.

"My daughter has said, 'You're making me feel like an outcast' " because her friends participate in "social networking websites" such as myspace.com, Ms. O'Beirne says.

"But I'm going to do everything I can to protect my child," she adds. "Whether she believes it's because we love her ... or we're trying to make her an outcast, when she's grown up she'll realize why we do what we do."

Finding the right balance between security and freedom, however, can be a challenge, many find.

Parents are right to "exercise an unusual amount of caution in this area because the damage can be so great," says the Rev. John Conley, a Fordham University professor of philosophy and frequent writer on the subject of rights and relationships within families.

Where cautious parents sometimes err, he says, is in adopting rigid computer usage rules that don't evolve as a child demonstrates responsibility and discretion.

"What can be damaging to the child is if, like, at the age of 18, the child is being bound by the same rules as in early adolescence," Fr. Conley says. "Children at some point ... are going to have to exercise their own judgment and their own freedom. [That won't occur] unless the parents are willing to relax the rules" at some point between ages 12 and 18.

One area youths can run into trouble with their own Web postings, according to Wiredsafety.org, is by menacing their peers.

Aftab gives a hypothetical example of bullying in a teenager who pretends to be another student by putting up a website, identifying the student as gay, and declaring a sexual preference for football players.

More common is lying to get access. Myspace.com, for instance, requires that participants be 16 or older; hence the scores of underage teens who use it have simply lied about their age to establish a site there.

Shannon Sullivan, for instance, says she did just that. Still, she didn't see the enterprise as dangerous until adults told stories about the potential horrors.

"I don't go in chat rooms," Shannon says. "I'm against talking to people I don't know [on the Internet]. But I just hadn't thought about what could happen at the myspace [blog]."

Lying about age should concern parents, Steinberg says, because it violates a trust code.

He also encourages families to "have a talk about Internet safety," and to put computers in public spaces in the home, where troublesome activity is less likely to occur.

Still, Steinberg says, while parents need to monitor Web usage by teens ("Is my child involved in something unlawful or dangerous?"), they also should accept that they won't always know everything about a child's life, especially as children become older teens.

"There are going to be lots of things that I don't know about [in my child's life], and that's OK," Steinberg says. "It's part of the development process."