In Britain, children aged between five and seven have been treated for anorexia or bulimia in the past three years, show figures.
The statistics show that 197 children aged between five and nine were treated in hospital in England for eating disorders, fuelling campaigners' fears that young children are being influenced by photographs in celebrity magazines.
The figures from 35 hospitals showed 98 children were aged between five and seven at the time of treatment and 99 aged eight or nine. Almost 400 were between the ages of 10 and 12, with more than 1,500 between 13 and 15 years old.
The statistics, released under the Freedom of Information Act, are believed to underestimate the true figures because some state-run hospitals refuse to release any data.
Other hospitals would only release figures for children admitted after they had become dangerously thin, excluding those undergoing psychiatric therapy as outpatients.
The findings come after experts called earlier this year for urgent action to improve the detection of eating disorders in children.
About three in every 100,000 children under 13 in Britain and Ireland have some sort of eating disorder, according to a study conducted by experts from University College London's Institute for Child Health.
Susan Ringwood, chief executive of the eating disorders charity B-eat, said the latest figures reflected "alarming" trends in society, with young children "internalising" messages from magazines which idealise the thinnest figures.
"A number of factors combine to trigger eating disorders. Biology and genetics play a large part in their development, but so do cultural pressures, and body image seems to be influencing younger children much more over the past decade," she said.
Children were receiving "pernicious" messages, Ringwood told the Sunday Telegraph.
"The ideal figure promoted for women is that of a girl, not an adult woman. That can leave girls fearful of puberty, and almost trying to stave it off," she said.
The Department of Health said it was spending Ģ400 million ($660 million, 455 million euros) over the next four years on psychological treatment for eating disorders, including a specific programme for children and young people.
"Early intervention is essential for those with eating disorders," a spokeswoman said.