Another study has found evidence that television viewing by young children is linked to aggression. The study appears an issue of Archives of Pediatrics & Adolescent Medicine.

The study found that direct TV watching by young children or exposure to indirect viewing in the household were both associated with increased aggression in small children.

tvAfter controlling the data for other factors, such as maternal depression, living in an unsafe neighborhood and being spanked, "for every hour that a child watched TV directly, aggression went up 0.16 on a scale of zero to 30. For a TV being on in the house, it was 0.09," said study author Jennifer A. Manganello, an assistant professor of health communication at the University of Albany School of Public Health, State University of New York.

And, she said, while the increase may not seem like a lot, when the researchers looked at all of the other factors, "TV was more likely than some other factors to increase aggressive behaviors."

The American Academy of Pediatrics (AAP) updated their policy on media violence.

"Exposure to violence in media, including television, movies, music and video games, represents a significant risk to the health of children and adolescents. Extensive research evidence indicates that media violence can contribute to aggressive behavior, desensitization to violence, nightmares and fear of being harmed," wrote the AAP Council on Communications and Media.

For the current study, researchers looked at data for 3,128 children born between 1998 and 2000. The children came from 20 large U.S. cities, and their mothers completed surveys when the child was born, and again at ages 1 and 3.

Because so many factors can influence a child's behavior, the researchers tried to control for as many factors as they could, including maternal health and depression, maternal parenting attitudes and behaviors, maternal experience with violence, the safety of the neighborhood and demographic characteristics.

The researchers found that children who were spanked, lived in an unsafe neighborhood or had a mother who was depressed or stressed were more likely to exhibit aggressive behaviors.

But, after controlling for these and other factors, the study authors found that TV -- both direct and indirect viewing -- had a statistically significant effect on children's aggressive behavior.

"A take-home message from this study is that parents should think about how much TV kids are watching themselves, but also think about the overall media environment in the home," said Manganello.

"TV is not a benign influence. It does have impact," said Richard Gallagher, director of the Parenting Institute at the New York University Child Study Center in New York City. And, while content may impact children, he pointed out that children's behaviors may also be affected by the "opportunities lost."

That means that when a child is watching TV, which is a passive behavior, the child doesn't have the opportunity to interact with other people and may have reduced contact with his or her peers.

"The AAP guidelines that children under 2 shouldn't watch any TV may be fairly strict and hard to carry out, but parents should be judicious about how much TV young children are watching, and be aware that it's not likely to be appropriately stimulating," he said.

He added that parents need to act as a TV filter for their children. For example, he said, parents should point out when something is silly on TV that it's not a real-life scenario. Or, if they see something violent -- say an anvil dropping on someone's head in a cartoon -- parents need to interpret that for their children, and let them know what would happen if that were a real situation.