The health risks for obese children may be even greater than previously estimated, new research suggests. So why do parents let their children get fat?

The recent start of the new school year was greeted with reports of a dramatic rise in demand for extra-large uniforms for primary school pupils.

It came as no surprise to Carol. Her two nieces were wearing size 14 skirts by the age of 11, the average size worn by a grown woman in the UK.

Her son also struggled to find a uniform big enough at secondary school as his weight crept up to nearly 20 stone (127kg) in his teens.

"You do feel judged by other people when your child gets to that size, but the harshest critic is yourself," says the mother-of-two from Birmingham.

"I constantly asked myself 'what am I doing wrong?'"

It's a good question. Just over 33% of 11-year-olds are now overweight or obese and among four and five-year-olds it's 22%, according to the most recent figures from the National Child Measurement Programme, which assesses the height and weight of primary children in England. The figures are similar in Wales, Scotland and Northern Ireland.

New research published today by the University of Oxford also suggests that obese children and adolescents have several risk factors for heart disease, including raised blood pressure and cholesterol, compared with normal weight children.

Obesity experts say parents are struggling with a multitude of problems when it comes to their child's weight. They range from a lack of education about food, limited cooking skills and limited money to buy healthier food to longer working hours and marketing campaigns for junk food aimed at kids.

But the more sedentary lives children now lead is also creating huge problems. Last week a study suggested that up to 75% of junior school children preferred to stay at home than go to their nearby park.

My mum wasn't the problem My problems started when I was between five and seven. When I was younger everyone said I had puppy fat and I would grow out of it - I didn't. By my teens I had a serious weight problem. People blame parents but my mum did everything she could she could to control my weight. I was very good at convincing myself and others that I wasn't eating very much. I would skip breakfast and lunch but make up for it at dinner. Sometimes I would secretly eat through the night. My mum would give me a good dinner because I said I hadn't eaten all day. She didn't want me to over eat but she didn't want me go without either Stacey, once over 25 stone (159kg) What are the health risks of obesity? Is this the ultimate healthy meal?

Watching TV was one of the most popular activities, with 89% saying it was how they liked best to spend their time away from school, according to researchers Lightspeed. In July, scientists from University of Montreal claimed every extra hour of television that a toddler watches each week adds to their waist size by the time they turn 10.

While the problems parents face might be increasing so is evidence about the dangers of obesity. So why do they let their children get so fat?

Katy's son weighed over 23 stone (147kg) by the age of 15. She knew the reason - he ate too much and did too little exercise. She says she tried to help him but things only changed after he decided to help himself.

"A lot of his eating habits were out of my control," says the mother-of-two from Buckinghamshire. "He would eat too much when he was at school and then come home and eat whatever was around, even cook big meals for himself. He wouldn't wait for me to get home and make dinner.

"I know I am not completely innocent when it comes to his weight. I have always struggled myself and have some bad eating habits, but I tried hard to change the way we both ate."

The turning point came on a holiday last year to the US. Her son was too big to go on certain rides at a theme park. Upset and humiliated, he went on a six-week weight-loss camp and lost nearly three stone (18kg). The camp was run by Wellspring UK, one of a number of firms offering camps in the UK.

"He had always refused to go before but now he wanted to. He is a different child now, so happy and confident. Before he had no self esteem and would have temper tantrums. His whole attitude to food has also changed, he now picks the right stuff to eat."

Some parents know they are a bigger part of the problem. Tracey says she allowed her daughter to pick up her own bad eating habits. Admitting to having a "complicated relationship" with food herself, she says she used it to bond with her daughter.

This starts with 'clean your plate' syndrome - my mother put down huge portions and made us carry on eating long after we were full Claire, Nottingham Childhood obesity: 10 of your stories

"We would snack together in the evening while watching television and treat ourselves with sweets and puddings. It was like our special time together," says the mother-of-one from Shrewsbury.

"I could see she was carrying a few extra pounds but she seemed happy. I didn't want to mention it because I didn't want her to feel negative about herself.

"When she started secondary she was almost 14 stone (89kg) and by then her bad habits were hard to break. I know I am responsible and I feel awful about it."

Despite the rise in child obesity, experts say it's wrong to just blame parents.

"They definitely have a responsibility, but the issue is much broader than simply blaming them," says Paul Gately, professor of exercise and obesity at Leeds Metropolitan University. He also runs weight loss camps for overweight children.

Many parents don't realise their child is fat when it might be obvious to other people, he says. According to studies, 75% of parents underestimated the size of an overweight child, while 50% underestimated the size of an obese child.

Media playback is unsupported on your device Media caption Chris Brewis a local councillor who says giving children fast food is abuse.

Even more surprisingly, a similar study of healthcare professions produced nearly the same results. It was carried out by Gately and his colleagues.

"A lot of it is because the images of obesity that we see in the media are people who are massive, 30 stone (190kg) or above. This is what a lot of people think of as being overweight, but they are extreme cases. It only takes a few extra pounds to actually be overweight."

People also judge things on what they see around them on a daily basis, Gately says. Tracey admits she let her daughter's weight creep up because "she was no bigger than some of her friends".

"Two thirds of adults in the UK are now classified as overweight, so our perception of what we consider the average size to be has changed," says Gately.

How many calories should you eat? 2,500 calories for men daily

2,000 calories for women daily

1,800 calories for children aged five to 10 daily Source: NHS Healthy living: How to live longer

Tam Fry, chairman of the Child Growth Foundation and spokesperson of National Obesity Forum, agrees.

"When trained health workers find it hard to pick out an average-weight child then you have to start to think we've got a problem and it's bigger than just what parents do."

The daily emotional battle around food can also be be fraught between a parent and a child.

"When I got hungry I would get so angry and scream and shout," says Stacey, a mother-of-one from London. "My mum would often end up shouting 'just have it then'. The pressure I put on her was huge and unfair, it put a real strain on our relationship."

She has struggled with her weight from the age of five. She reached nearly 20 stone in her teens.

"My mum did everything she could think of to help me, enrolling me in sports classes and trying to get professional help. She even went to my school to tell staff what I was and wasn't allowed to eat, but the problem was me."

From a very early age children are very good at using a "whole set of behaviours" to get what they want, say experts. It's easy to judge but nearly every parent in the land has caved in to some sort of emotion blackmail from their child, says Gately. It just might not be about food.

The expert's view Despite all the talk about tackling child obesity, the reality is there is very little professional help out there. Most dietetic services will not see obese kids because they don't think they can be effective. They know losing weight is about more than just the diet. We clearly need an approach that combines diet, exercise, education and psychological support. Obesity expert Professor Paul Gately

Charlie Powell, campaigns director of the Children's Food Campaign - an alliance of 150 education bodies, health groups and children's charities - says it's also hard for parents to stand up to the barrage of junk food advertising.

"There are huge hurdles they have to surmount to keep their children healthy. It's stuff that wasn't around in years gone by and food manufacturers are very sophisticated in the techniques they use to appeal to children."

Katy's son, who is still 15, has lost another 3kg (6lbs) since coming home from camp. Carol's son eventually went on a weight-loss programme and lost about five stone (32kg). Now 27, he has kept it off.

Stacey had a gastric band fitted three years ago, at the age of 25, and is now 14 stone (89kg). She says she will work hard not to pass on her problems with food to her four-month -old daughter as she grows older.

Tracey is continuing to help her daughter, who is now 15.

"We're trying hard and being much healthier, but she will probably be watching her weight for the rest of her life, just like me. I feel awful about that."

Many of you got in touch with stories of your childhood obesity. Here are 10 of your tales.