Parents and doctors who view food fussiness as a passing phase could be making a grave mistake, a study suggests.
Even moderate pickiness was associated with significantly increased levels of depression and anxiety in a population of more than 3,000 children aged two to six.
Those with highly selective eating habits were more than twice as likely as normal eaters to have a diagnosis of depression.
Lead researcher Dr Nancy Zucker, director of the Duke Centre for Eating Disorders in the US, said: "The question for many parents and physicians is: when is picky eating truly a problem?
"The children we're talking about are not just misbehaving kids who refuse to eat their broccoli."
The study, published in the journal Pediatrics, found that more than a fifth of the children were selective eaters. Of these, nearly 18% were classified as "moderately picky" and about 3% as "severely selective".
Children with both moderate and severely selective eating habits displayed symptoms of anxiety and other mental problems.
Dr Zucker added: "These are children whose eating has become so limited or selective that it's starting to cause problems. Impairment can take many different forms.
"It can affect the child's health, growth, social functioning, and the parent-child relationship. The child can feel like no one believes them, and parents can feel blamed for the problem.
"There's no question that not all children go on to have chronic selective eating in adulthood. But because these children are seeing impairment in their health and well-being now, we need to start developing ways to help these parents and doctors know when and how to intervene."
Some children who refuse to eat might have heightened senses, causing them to be overwhelmed by the smell, texture and taste of certain foods, she pointed out.
A bad experience with a certain food could lead to anxiety when a child is given something else that is new and untrustworthy.
New remedies were needed for sensitive children with frequent experiences of "palpable disgust", said Dr Zucker.