Depression, with its recurrent, long-lasting symptoms and complex of medications, is a particularly brutal diagnosis for a young child. “Mood disorders are scary to acknowledge, and depression is especially scary,” says Mary J. O’Connor, a child psychologist, professor and founder of the infant and preschool clinic at U.C.L.A. “When we sit down with a parent and give them a diagnosis of depression, they have this fatalistic idea of something devastating and terrifying and permanent.”

And parents tend to feel responsible. Children of depressed parents are two to three times as likely to have major depression. Maternal depression in particular has been shown to have serious effects on development, primarily through an absence of responsiveness — the parent’s conscious and consistent mirroring and reciprocity of an infant’s gaze, babble and actions. “Depressed mothers often respond to their babies from the beginning in ways that dampen their enthusiasm and joy,” says Alicia Lieberman, a professor in the department of psychiatry at the University of California, San Francisco. This is problematic, as 10 to 20 percent of mothers go through depression at some point, and 1 in 11 infants experiences his mother’s depression in the first year.

But it’s easy to overstate the role of maternal depression. “Most kids of depressed parents don’t get depressed,” says Arnold Sameroff, a developmental psychologist at University of Michigan’s Center for Human Growth and Development, who has studied children of parents with mental problems. Conversely, parents need not be depressed to heighten depression in their children. “There are definitely situations where the family interaction is creating the negativity in the child’s life, and that is one pathway to depression,” says Tamar Chansky, founder of the Children’s Center for O.C.D. and Anxiety in suburban Philadelphia. “But what I see more often is the no-fault situation, where parents are baffled to hear such negative thoughts coming from their children.” Despite the assumption that these kids must have experienced severe psychosocial deprivation, abuse or neglect, Luby says: “I’ve seen many depressed kids with nurturing, caring parents. We know that psychosocial stress is an important ingredient, but it’s not the only issue. And it’s not a necessary condition either.”

Kiran’s parents have advanced degrees and stable jobs and were invested in being good parents. Both participated in a Missouri’s Parents as Teachers program, receiving instruction during Kiran’s first three years. But Elizabeth says she does wonder if her behavior exacerbated some of Kiran’s negative tendencies. “Sometimes I worry that we were too critical of Kiran,” Elizabeth told me over the phone in January. “I was exasperated with him all the time. I wasn’t intentionally trying to make him feel guilty, but the way I was interacting with him was providing a guilt trip.” Elizabeth’s own moods sometimes played a role. “If my mood was low, his got even lower.”

IN A SMALL LAB slightly off the main campus of Washington University in St. Louis’s School of Medicine, Joan Luby is trying to figure out exactly what constitutes preschool depression. For a new clinical diagnosis to gain sanction with psychologists, schools, doctors and insurance companies, it requires entry into the Diagnostic and Statistical Manual of Mental Disorders, the field guide to psychiatric illness. Though the manual, last thoroughly revised in 1994, purports to describe and classify the full range of mental disorders, it was not designed to capture preschool conditions. To help practitioners recognize problems earlier, the research organization Zero to Three published its own manual, the Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood, most recently in 2005. But its methods of review aren’t as rigorous as those in the D.S.M., and many await the imprimatur of the updated D.S.M., due in 2013, which is expected to account for developmental stages of disorder across the lifespan.

Luby is one of the first researchers to systematically investigate the criteria for preschool depression, primarily through a longitudinal study that initially evaluated children between ages 3 and 5 for depression and was financed by the N.I.M.H. These children, who are now between 9 and 12, come into a lab every year for assessments. Offshoot studies have looked at everything from the role of tantrums in depressed children to how depressed preschoolers perform on cognitive tasks. Luby’s file cabinets teem with DVDs of each of her study participants’ periodic assessments. I watched one recording in which a 5-year-old squirmed in her chair while her parents answered questions. “She cries at the drop of a hat.” “She realizes that something’s different about her, and she’s bothered by her irritability and sadness.” “At times she’ll accept comfort; other times, nothing will console her.”

Through interviews like this, Luby is trying to identify preschool depression’s characteristics; according to her research, they look a lot like those in older people. In adults, for instance, anhedonia, the inability to derive pleasure in normally enjoyable activities, can be signaled by the absence of libido; in preschoolers, it means finding little joy in toys. Other symptoms, including restlessness and irritability, are similarly downsized. These kids whine and cry. They don’t want to play. Rather than voice suicidal ideation, they may orchestrate scenarios around violence or death.