WEDNESDAY, March 2 (HealthDay News) -- Countering the belief that you have to be "older" to suffer from mental illness, a new report says there's actually no lowest-age limit.

Infants and toddlers can be affected, but they often go without treatment that could prevent them from suffering long-term problems, according to the researchers.

There's a "pervasive, but mistaken, impression that young children do not develop mental health problems and are immune to the effects of early adversity and trauma because they are inherently resilient and 'grow out of' behavioral problems and emotional difficulties," they wrote in the February issue of American Psychologist. The issue includes a series of articles about mental health in children under the age of 5.

In fact, infants can develop mental health problems as they deal with their goals and emotions, the authors of another article wrote.

"Infants make meaning about themselves and their relation to the world of people and things," they said, but that process can go wrong. "Some infants may come to make meaning of themselves as helpless and hopeless, and they may become apathetic, depressed and withdrawn. Others seem to feel threatened by the world and may become hyper-vigilant and anxious."

In a third article, researchers reported that insurance may not cover mental health treatments for kids younger than 3.

What to do? Researchers from Louisiana State University and the University of California, San Francisco advocate more early screening, better training and education of people who deal with children. They also urge better coverage by private insurers and Medicaid.

More information

The U.S. National Institute of Mental Health has more on children's mental health.