Recently, Janet Kotowski's 9-year-old daughter, Elizabeth, and Elizabeth's little sister, Jennifer, started dabbling on the Internet, always with their parents at their side.

With the clicks of a mouse, the Gaithersburg family has harnessed a wealth of information for school assignments, downloaded art project ideas from Crayola's Web site and learned about their favorite exotic animals on the Kratts' Creatures pages.

Kotowski knew not all sites were so family-friendly. But last week, she got a shocking glimpse at the very real dangers the virtual world can hold.

At a meeting of the Thurgood Marshall Elementary School's PTA, a police officer demonstrated how innocent searches can turn up pornographic or violent Web sites. Then he told stories of youngsters who were lured into giving personal information to sexual predators who troll online chat rooms.

"I don't think I'm unaware but . . . the thing is just how scary it can be," Kotowski, 41, said. "People don't expect kids to get into this stuff, and they do."

As more and more children have access to the Internet -- a recent report by the New York research firm Cyber Dialogue shows that about 10 million children spend time online at home now, compared with about 4 million in 1995 -- police have started adding Internet safety to the topics they regularly include in crime prevention programs.

Prince William County police in January began offering Internet safety tips at PTA meetings. Fairfax, Montgomery and Arlington police also have been making the rounds of local PTAs and community groups. And the Loudoun County Sheriff's Office is offering its first Internet safety program this week.

While officers preach that children should abstain from drugs and alcohol and ignore strangers, helping children avoid the dangers that lurk on the Web is not as simple as "just say no."

Prince William police Sgt. Steve Hudson said that when he's talking to parents, he often shares an analogy he heard from a computer engineer. "It's like letting a child alone in the city," Hudson said. "There are a lot of wonderful things he can do. He can go to museums or learn about the government. But he also can fall prey to people out there and get into all kinds of trouble."

Officers explain how search engines work and the basics of filtering software. They also offer some standard safety suggestions: Keep the computer in a family room where it's easier to monitor online activity, teach children they should never give out personal information and don't let the computer become a "babysitter."

"I tell parents there's no free lunch," said Montgomery County police Cpl. Brian Ford, a computer crimes investigator. "You must spend time with your child at the computer. Parents have to be aware."

Cathy Hussain, of Lake Ridge, attended a program that Prince William police held for the Antietam Elementary School PTA last month because her daughters, aged 9 and 11, are beginning to experiment online.

Hussain, 36, who works part time for an environmental group, said it wasn't until a week later that the lesson really hit home. "Something came up about school uniforms, and another PTA member searched `school uniform' and there was this porn site," she said.

While most agencies gear their presentations toward adults, the Loudoun County Sheriff's Office will try a slightly different approach. Its class will involve both parents and children, to give families a starting point to discuss the benefits and the downside of the Internet.

"I liken it to when a parent wants to sit down and talk about the birds and the bees or drugs, and there's that initial hesitance," Loudoun investigator Robert Weitershausen said. "They are important issues, but you don't want to turn the children off when you broach the subject."

In the course of his job, Weitershausen helps handle the growing stream of search warrants filed in Loudoun by investigators nationwide seeking information from Dulles-based America Online. He said he toyed with the idea of starting the safety program after reading case after case about predators who use the Internet to find young victims.

Then came the Columbine High School shooting. As news reports of the Littleton, Colo., shooting detailed Web sites where one of the killers posted bomb-making instructions and a sketch of a young man firing two guns, parents nationwide began expressing heightened concerns about the dark side of the Web.

"We've been getting inquiries from people who say, `My kid accessed this or that. How do we stop this?' " said John Patton, chief deputy in the Loudoun Sheriff's Office.

Those calls, Weitershausen said, gave him a final push to get the program running. The first class is scheduled for Wednesday, with two more later in the month.

Weitershausen said he'll start the 1 1/2-hour sessions with an overview of the Internet. "We'll talk about education, sports, hobbies, communication with family and friends," he said. He's also including sites that are sexually explicit or contain violent material.

Weitershausen's students also will hear a fictitious story about an 11-year-old girl named Zoe who is tricked into giving personal information to a "boy" she meets in a chat room. The boy, the children and their parents will learn, is really a 40-year-old pedophile.

Fairfax County computer crimes detective Ken Haynes said he's kept his presentations to adults because he worries that giving too much technical information to children might teach them to hide some online activity from less-savvy parents.

"If you bring them in the room and tell them the exact same thing," Haynes said, "the kids are going to know what you are watching for and get around it."

But regardless of the approach, law enforcement officials agree that the key to preventing kids from inappropriate or dangerous activity online is to keep parents involved.

Hussain, the Lake Ridge mother, said she encourages other parents to keep close watch on their children's online activity.

"It's something parents need to be made aware of," Hussain said. "The parents out in Littleton, how much did they know? And the ones in Conyers, how much did they know? And how dumb are we?"