The influence of media on children's behavior has been studied since the 1950s. Adolescents who are exposed to more media tend to drink at a younger age. Those who watch more violent fare are found to be more aggressive when given punching toys, Robinson said.
Conversely, according to recent experiments, children who spend less time on electronic devices are less aggressive on the playground, he said.
Though most studies have focused on television, Robinson said he expects similar findings with digital media.
Robinson's research has also focused on family rules about media access.
When parents are asked if they have rules at home, 80 percent say they do, but only 50 percent of kids say they are restricted at home, he said.
"Parents think they have rules, but kids have to know (the rules) exist," he said. "Kids do best when they have limitations on them — when they know the rules. It's a child's job developmentally to find out what is acceptable and what isn't."
Unfortunately, 70 to 80 percent of kids have a television in the bedroom, away from parents' eyes and ears, he said. Studies show a link between the amount of screen time, social development and scholastic scores. Robinson said that could be significant.
"What's scary is that studies show ethnic minorities and lower-income kids are more likely to have the technologies in the bedroom. In many ways, it's creating a greater disparity, an even wider educational gap," he said.
Digital media is also shifting kids' understanding of how to connect, said Holly Pedersen, director of community education programs at Jewish Family and Children's Services' Parents Place, which offers classes on child development and the use of digital media.
Teachers complain that digital media are so stimulating and responsive that students don't listen well when someone simply speaks in front of a classroom, she said.
"You're not having flashing lights that reward you. Teachers say they have to be an entertainer now."
Some studies found excessive screen time could lead to delays in the development of language and grammar skills, she said. The American Academy of Pediatrics recommends that children under age 2 have no exposure to any screens, she added.
As children move through adolescence there are other concerns. Digital media raise issues about how children are learning the meaning and development of friendships: "What does it mean when someone is 'liking' your post?" she said.
Susan Stone Belton, a family coach and motivational speaker in private practice, teaches classes at Parents Place on breaking free of electronic devices and setting limits. Kids — and adults — become addicted to electronic devices for different reasons at different ages, she said.
"As tweens and teens, they're really addicted to connections. Teens are so afraid they will miss something," she said.
Digital-media use should have a context, Pedersen said. Devices should not be babysitters because kids are cranky and have nothing to do.
Parents play a big role in regulating their child's exposure to media, including the amount of control a child can have over content and screen time.
"Parents do need to be monitoring what kids are doing, at least through early high school. Make it a condition of using the device. Tell your kids, 'I'll be monitoring what you are posting,'" Pedersen said.
Parents should be clear about the rules and stick with them, Belton said.
"Your child will say: 'All of my friends have a cell phone,' or 'None of my friends are being restricted.'
"That's when you say: 'Then it must be hard to be the only one your age, but in our family you're not getting a (fill in the blank). That's the rule we have in our family.'
"Validate it, but be empathetic," she said.
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