FOUR in 10 children who were treated for obesity by hospital specialists already had risk factors for heart disease.
The 312 children were referred to the weight-control programme in Temple Street Hospital in Dublin, and were all under the age of 16.
Some children were nearly nine stone in weight when seen and all were classified as obese.
One in three of the children already had complaints such as knee pain and breathlessness when walking.
Six in 10 had psychological problems such as poor self-esteem and depression and more than one in 10 suffered severe bullying.
Consultant paediatrician Dr Sinead Murphy said the children ranged from 18 months to 16 years of age, but the youngsters are mostly in middle childhood when referred.
"The older we see them, and the higher the overweight problem, the most likely they are to have risk factors for heart disease such as high cholesterol. They can also have insulin resistance which pre-disposes them to diabetes."
Dr Murphy said children can end up putting on weight because they are surrounded by a "toxic environment" where they have to make a conscious effort not to eat unhealthy foods.
This is combined with lack of exercise which can be exacerbated by safety issues, such as not walking to school.
The W82GO! programme involves a multi-disciplinary team of specialists including a paediatrician, physiotherapist and psychologist to help tackle what can be a complex change of lifestyle for the youngster.
Physiotherapist Grace O'Malley said: "We introduce families to how they can make small goals to becoming healthier."
The service currently has a waiting list of 150 children who have to wait several months before being seen. Dr Murphy said the fear is that the children will put on more weight during that time and may have lost the motivation to make changes.
Celine Dixon from Finglas in Dublin, whose daughter Lily (8) was six stone last summer when she started the programme learned of the benefits of portion control.
Lily has become one of the programme's successes. She has her weight under control and is getting taller.