Doctors may be failing to spot tell-tale signs in children who are underweight, a study suggests.
A University College London team spoke to paediatricians at 177 hospitals in England and Wales and found poor knowledge on identifying underweight children and serious complications.
This was despite most respondents having experience of treating a child with an eating disorder.
The Royal College of Paediatrics said it was working to improve training.
Study leader Dr Lee Hudson from the Institute of Child Health, University College London, said more under-13s now presented with eating disorders than meningitis due to the success of vaccination programmes.
This shift in childhood illness may be one reason why his research suggested a lack of knowledge on spotting underweight children and the associated medical problems, he added.
In the study, one on-call paediatrician was questioned in every hospital providing acute in-patient care for children.
During a phone interview they were asked how they would identify if a child was underweight and what clinical examinations they would carry out to check for severe or potentially life-threatening complications.
Only half said they would use Body Mass Index to decide if older children or adolescents were underweight, as advised in international guidelines.
And only one in five said they would adjust that for appropriate cut-offs in children.
There was also a lack of awareness of signs and symptoms of complications in children whose weight had dropped to seriously low levels.
The researchers were particularly concerned that only 13% knew a specific danger sign to look for in tests checking that the heart was working properly, the team reported in Archives of Diseases in Childhood.
Doctors also scored poorly on knowledge of dangerous complications associated with giving nutrition to someone who has not eaten for a while or is severely malnourished.
Dr Hudson said this was not a criticism of doctors because eating disorders tended to present with vague symptoms, but highlighted a gap in training.
"In addition to that, services for children with eating disorders are very hit and miss around the country."
But he stressed that as those surveyed would be the first paediatricians to assess such children, especially out of hours, they needed to know how to spot dangerously underweight children and teenagers and signs of severe complications.
"From previous research we know that a third of children who are underweight present with life-threatening features," he added.
Prof Russell Viner, a co-author of the study but also a member of the Royal College of Paediatrics Nutrition Committee, said the college was aware there was a training need around eating disorders and underweight issues.
"We are refreshing training on adolescent health," he said.
"And in association with the Department of Health and the Royal College of Psychiatry we are developing a training programme around mental health in adolescents."