(CNN) -- For years, pediatricians have recommended that young children watch no TV, or as little as possible, because it can lead to problems in school and behavior issues. Now a new study concedes children are sitting in front of the TV a lot longer. However, controlling what they watch can improve how they behave.
When preschoolers watch educational programs instead of violent TV shows, they tend to be more compassionate and less aggressive, according to a study published Monday in the journal Pediatrics.
About 600 families were recruited and assigned to one of two groups. Parents in the first group were encouraged to substitute violent shows with educational and pro-social ones - shows that stressed compassion and cooperation.
Families were given monthly TV guides listing educational programming for their area: shows such as "Dora the Explorer," "Super WHY," "Sesame Street" and "It's a Big, Big World." Parents were also encouraged to watch TV with their kids.
The children went from watching a half-hour of violent programming a day to 23 minutes. Parents then increased educational viewing from about 30 to 43 minutes a day.
Families in the second group did not change their viewing habits.
"This is the first study to try to modify the viewing habits of preschool kids," says Dr. Vic Strasburger, spokesperson for the American Academy of Pediatrics. "That's one of the significances of this study."
After a year, researchers found that children watching less violent and more child-appropriate shows scored better on tests that measured cooperation, a willingness to share or compromise. They also had fewer incidents of aggressive behavior such as yelling and hitting.
"Although television is frequently implicated as a cause of many problems in children, our research indicates that it may also be part of the solution," the study notes.
The scientists saw the greatest improvements in boys raised in disadvantaged homes where children tends to watch more TV.
Experts know that children mimic what they see, whether it's in real life or what's on the screen. And this is of particular concern when children watch TV or movies riddled with violence.
"Children learn their attitudes about violence at a very young age, before age 8 and once they learn those attitudes it's very difficult to unlearn them," says Strasburger.
"It doesn't mean that children who watch violence are going to become murderers, but it does mean that they are desensitized to violence in the real world and they are more likely to be aggressive themselves," says study author Dr. Dimitri Christakis, director of the Center for Child Health, Behavior, and Development at Seattle Children's Research Institute.
Better shows, better kids
But on the flip side, when children watch shows with positive social messages, it helps them get along better with others and gives them the tools to become better communicators, the study suggests.
"They will imitate the good things too," says Christakis. "We should take more advantage of the fact that you can demonstrate good behaviors on-screen and that children will emulate them in real life."
Right now, the American Academy of Pediatrics recommends that preschoolers and older children get only one to two hours of TV or screen time a day. But in reality, they're really watching much more. According to this study, preschoolers see an average of about four and a half hours daily at home and in daycare settings. Parents struggle with guilt, researchers say, because they allow so much TV time.
"Parents need to get this message that it's not just about how much TV your children watch, it's about what they watch," says Christakis. "It's not just about turning off the set; it's about changing the channel."