“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.

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.

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. 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.”

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By Denise Winterman
BBC News Magazine