Chicago ? Depression in children as young as 3 is real and not just a passing grumpy mood, according to provocative new research.

The study is billed as the first to show 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 6,” said lead author Dr. Joan Luby, a psychiatrist at Washington University in St. Louis. “They didn’t think it could happen … because children under 6 were too emotionally immature to experience it.”

Previous research suggested that depression affects about 2 percent of U.S. preschoolers, or roughly 160,000 youngsters, at one time or another. But it was unclear whether depression in preschoolers could be chronic, as it can be in older children and adults.

Luby’s research team followed more than 200 preschoolers, ages 3 to 6, for up to two years, including 75 diagnosed with major depression. The children had up to four mental health exams during the study.

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. Overall, nearly 20 percent had persistent or recurrent depression at all four exams.

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, funded by the National Institute of Mental Health and released 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 Dr. 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.

And, in fact, Luby said she has separate, unpublished research showing that chemical changes seen in older children also occur in depressed preschoolers.

Dr. 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.