CHILDREN as young as four are being hospitalised for eating disorders after refusing to eat and going on dangerous diets in their quest to be thin.

The largest eating disorders clinic in NSW, based at The Children's Hospital at Westmead, has reported a 270 per cent spike in the number of children being admitted to hospital over the past decade.

Even more alarming is the rise in the number of children being treated as outpatients at the hospital - it has increased more than 10-fold, up from 298 in 2003 to 3157 in 2009.

Clinic co-director Dr Michael Kohn said patients are getting younger.

"The average age for presentation is decreasing and the reason is the stress on young people has increased, so that those people vulnerable to develop eating disorders are doing so at a younger age," Dr Kohn said.

On Thursday alone, Dr Kohn saw 12 new patients including a five-year-old.

Dr Kohn identified several factors driving down the age of patients with eating disorders including media portrayal of thin women and cute men as attractive ideals, the amount of food advertising targeting children, and that the children of obese parents don't want to end up like them.

"The fact that children have obese parents and don't want to get fat, wanting to be healthy but in the process diet and lose weight unhealthily, leading to the development of eating disorders - it's a group we haven't seen before," Dr Kohn said.

The average age of girls reaching puberty had also decreased, resulting in the sexualisation of girls at a younger age and making them more vulnerable to body image issues.

Commonly a child will start to diet or lose weight as some form of body comparison at school, or they'll be learning about healthy eating at school.

Relationships not working out and the desire for popularity can also drive eating disorders in children.

Christine Morgan, chief executive of eating disorder charity The Butterfly Foundation, said girls were suffering from negative body image issues from an earlier and earlier age.

"To be on a diet is an everyday thing and there are numerous consequences to normalising this behaviour, especially for young people," she said.

"Young people are being influenced by their peers and the social media that their appearance equals their value and therefore there is merit in being slim."

Dietician Arlene Normand said eating disorder numbers had reached critical levels.

"There are not enough beds available for the number of children we're seeing with eating disorders," Ms Normand said.

She said mothers who skipped meals, embarked on crash diets and visited the gym too often were poor role models for their impressionable children.

"I'm seeing a lot of children now who are being bullied at school due to obesity, and very often these obese children become anorexics due to bullying," Ms Normand said.

"It's very hard sometimes to teach them to be moderate," she said.

A recent study of 482 NSW school students aged 14 to 17 by the Australia Research Institute at Sydney Adventist Hospital found 54 per cent of girls had dieted, with 11 per cent doing so "often".

The survey also revealed 28 per cent of schoolgirls skipped meals to control their weight and seven per cent used self-induced vomiting to control or reduce their weight.

Originally published as Children 'too afraid to eat'