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
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