In Friday's episode of '20/20,' Elizabeth Vargas examines what some experts call digital addiction

Parents might not always be aware of what their children are doing on their communication devices, but experts say there are obvious signs when it’s becoming dangerous.

In Friday night’s 20/20, Elizabeth Vargas investigates the symptoms of what some mental health professionals call digital addiction — and the questions parents need to ask.

“Is it interfering with school? Are you getting bad grades? Is it interfering with their functioning?” says Dr. David Rosenberg, department chair of psychiatry at Wayne State University and the Detroit Medical Center. “Or they’re breaking things, or they’re fighting with you, they’re hurting themselves, they’re refusing to go to school, they’re not sleeping at all, they’re gaining a massive amount of weight.”

For more than a year, 20/20 followed families in the “depths of their struggle,” exploring the “destructive dependence, extreme change of personality, isolation, and physical signs during withdrawal” victims can experience, ABC said.

The special examines the cases of a 15-year-old girl who went to rehab after a dangerous online relationship; a 14-year-old gamer whose obsession prevented him from attending school; and a man’s excessive gaming habit that severely impacted his wife and four children.

Kevin Roberts, author of Cyber Junkie and Escape the Gaming and Internet Trap, says parents with children in similar situations should take action “when you have a child that you can’t trust, who time and again will not follow the rules, lies, covers up the behaviors.” And pay attention to “emotional outbursts when you turn off the game or take the smartphone,” he cautions. “That’s a red flag.”

But don’t go it alone. “The most important thing, if you’re concerned, is to get a comprehensive assessment by a trained professional, a mental health professional,” says Rosenberg.

.To stop bad habits from forming, Roberts advises parents to be careful early on. “We want to start considering screen use from a very young age,” he says. “Children under 7, I’d severely limit it. I would not use technology as babysitters.”

He adds: “Require outdoor activities, sports, performance in school as requisite behaviors that you have to accomplish and achieve in order to use technology.”

Considering the example you’re setting is also crucial: “You have to be the model,” says Roberts. “You have to model the behaviors that you want in your children.

20/20 airs Fridays at 10 p.m. ET. Watch the clips above for a preview of Vargas’ special.