Jenny was only 8 years old - too young to be sad. But there was no sparkle in her dark eyes, no liveliness in her face, no energized look to her body.

Jenny's parents noticed her listlessness, her despondency early on. "Even as a toddler we used to coach her to brighten up by saying: `Jenny will be a happy girl,' " says her mother."Jenny was always the most sensitive of our children, the one with the least confidence, and the one most easily squashed," her mother said.

"We always had to treat her with kid gloves. One minute we could reason and talk with her; the next, she would be angry and unreasonable. And the problem was always someone else's fault."

Jenny's parents sometimes attributed her behavior to being a middle child who was "just seeking attention." But her behavior made them uneasy. She was the child who would say, "Nobody likes me. I don't have any friends. I wish I were dead."

Jenny's parents worked hard to buoy her self-esteem. "We might, for example, help Jenny write out a list of 40 things that were positive about her and post it in her room."

But Jenny's moods continued to vacillate between sad and angry, and she remained hard to manage.

By the third grade, added to Jenny's moodiness were complaints of headaches and stomachaches and balkiness at going to school in the mornings. Finally, when Jenny was late for school the third day in a row, having left home crying hysterically, her mother realized Jenny was a child experiencing real despair. She sought help.

A professional diagnosed Jenny as suffering from a childhood disorder often unrecognized by adults: depression.

"It's not the temporary, easily shaken kind of blues that most children occasionally experience, but a deep, pervasive, persistent unhappiness that paralyzes emotional growth and social development," says Alice Lake, author of the article "Childhood Depression - the `Killer' Blues" (Women's Day, June 1983).

Some 400,000 to 500,000 children suffer some form of depression. Early diagnosis and treatment will usually restore a child to emotional and psychological health in a relatively short time. However, says Lake, about half of the cases of childhood depression go unrecognized or untreated and may result in severe long-term illness, even suicide among children as young as 5.

"Such tragic oversights stem from our traditional rosy picture of childhood as joyous and carefree. Adults find it difficult to accept the idea that a child may be deeply depressed," Lake observes. "The frequent reaction of parents and pediatricians is, `Don't worry. It's just a phase. He'll grow out of it.' "

Depression in children is often triggered by extreme stress or loss. Children may also inherit a genetic predisposition to the disorder and become depressed for no apparent cause. If depression afflicts one parent, chances are two out of five that children will also suffer the same disease. Because the reasons for depression are so complex, parents should never assume a child's depression is their fault.

Adults can recognize depression by looking for these signs, together which often constitute a distinct personality change in children:

- Pervasive sadness. Depressed children laugh little and cry a lot; their voices may be soft with little inflection. They have little interest in any activity and may appear to have a solemn maturity beyond their years. They may also become more hurt more often than other children.

- Irritability and negativity. Children are touchy and their anger is often irrational and triggered by the smallest of irritants. They are often viewed as "stirring up trouble" in families and may constantly fight with siblings, who are set off by their irritability.

- Sleep disturbance. Children often have difficulty falling asleep or staying asleep, and they may have recurrent nightmares. Occasionally, when children reach the teen years, their sleep disorder takes the form of oversleeping.

- Difficulty concentrating. Because children lose their ability to comprehend and pay attention, school grades often plummet; a teacher may report daydreaming.

- Lowered self-esteem. Depressed children often refer to themselves as dumb or ugly. One adult, recalling her depressed childhood, says: "I remember crying on my bed and singing, `Everybody hates me, nobody loves me, I guess I'll go eat worms.' "

- Guilt. They may feel guilty for weeks over a minor mistake and apologize for incidents that were not their fault.

- Physical complaints. They may also have frequent stomachaches and headaches and mistake their feeling of depression in the morning for "flu."

- Preoccupation with death. Persistent preoccupation over the health of a parent, the death of a pet, or frequent nightmares about people dying are signs of depression - and sometimes suicidal thinking.

- Regressive behavior. Children may regress to more babyish ways, to bed-wetting, temper tantrums and clinging or irritable behaviors.