The study is billed as the first to show that major depression can be chronic even in very young children, contrary to the stereotype of the happy-go- lucky preschooler.

Until fairly recently, "people really haven't paid much attention to depressive disorders in children under the age of six," said lead author Joan Luby, a psychiatrist at Washington University in St Louis. "They didn't think it could happen ... because children under six were too emotionally immature to experience it."

Luby's research team followed more than 200 preschoolers, ages three to six, for up to two years, including 75 diagnosed with major depression.

Among initially depressed children, 64 percent were still depressed or had a recurrent episode of depression six months later, and 40 percent still had problems after two years.

Depression was most common in children whose mothers were also depressed or had other mood disorders, and among those who had experienced a traumatic event, such as the death of a parent or physical or sexual abuse.

The new study, released on Monday in the August issue of Archives of General Psychiatry, did not examine depression treatment, which is highly controversial among children so young. Some advocates say parents and doctors are too quick to give children powerful psychiatric drugs.

Though sure to raise eyebrows among lay people, the notion that children so young can get depressed is increasingly accepted in psychiatry.

University of Chicago psychiatrist Sharon Hirsch said the public thinks of preschoolers as carefree. "They get to play. Why would they be depressed?" she said.

But depression involves chemical changes in the brain that can affect even youngsters with an otherwise happy life, said Hirsch, who was not involved in the study.

"When you have that problem, you just don't have that ability to feel good," she said.

Helen Egger, a Duke University psychiatrist who also has studied childhood depression, said it is common among people in her field to first see depressed kids in their teens.

Their parents will say symptoms began very early in childhood, but they were told, "Your child will grow out of them," Egger said.

Typical preschoolers can be moody or have temper tantrums, but they quickly bounce back and appear happy when playing or doing everyday activities. Depressed children appear sad even when playing, and their games may have themes of death or other somber topics. Persistent lack of appetite, sleep problems, and frequent temper tantrums that involve biting, kicking or hitting also are signs of possible depression, Egger said.

University of Massachusetts psychologist Lisa Cosgrove said she is skeptical about the accuracy of labeling preschoolers as depressed, because diagnostic tools for evaluating mental health in children so young are not as well tested as those used for adults.

And Cosgrove said that while early treatment is important for troubled children, "we just have to make sure that those interventions aren't compromised" by industry pressure to use drugs.

Research has suggested that rising numbers of preschoolers are taking psychiatric drugs, including Prozac, which is used to treat depression.

ASSOCIATED PRESS