The self-consciousness of a pre-teen is something many parents are only too aware of and the dreaded question of "Am I too fat?" can leave many lost for words. Even a carefully phrased response can provoke prolonged silences or slammed doors.
Fears that focusing attention on a child's size might make them overly self-conscious, cause them to obsess about their appearance, or even lead to an eating disorder may cause parents to shy away from the topic.
There is no single strategy, but there are "common sense" ways to deal with such a touchy issue.
First, you have to talk about it
Some parents think that the less said the better but there is no barrier to talking about things with your child, says Andrew Hill, professor of medical psychology at the University of Leeds's institute of health sciences.
"It's not easy," he says, "but if questions are raised, don't duck them. Be engaged. The key thing is the 'why'. I would want to know why this behaviour is suddenly occurring. Is it something the child has seen on TV, or has someone said something at school - maybe something subtle but hurtful. These concerns are often symptoms of other events - sort these out and the other behaviour will likely moderate itself."
A child's weight concerns, he says, often fluctuate and can be temporary.
Girls of a particular age - coming up to puberty - do compare themselves with others in the class, he says. The most rapid change for a girl's body is growth associated with puberty and there could be massive differences within a single class.
Girls, on average, double the amount of body fat as they go through puberty. Boys' body composition changes, but in a different way: they tend to put on more muscle, he says.
"When girls compare themselves, they are at different points of their physical development. Talking to them is a positive and reassuring way to deal with it. Let them know that in a few years' time, those physical differences would have reduced. The key is not to make them self-judgemental."
Don't be alarmed
A parent should not overreact if a child asks them whether they are fat, says Paul Gately, professor of exercise and obesity at Leeds Metropolitan University. "There are parents who are absolutely gobsmacked. It's the dreaded question that's come when they are not prepared. But their reaction might cause a child to think "what have I unleashed?" says Gately.
Many parents, he says, will "stick their heads in the sand" or tell a child there isn't a problem. But, he says, if there is a problem, the child will get teased in school and end up mistrusting the parent.
"The teasing and bullying of overweight children is endemic in our schools," he says.
"If a child has mentioned it, the issue is not going to go away. Parents need to have an open-ended, conversations in which the children do the talking. The child needs to understand it from their perspective," he says.
With child obesity on the rise, parents who have concerns that their child might be overweight could prepare in advance for the conversation that will inevitably come, says Gately, who runs weight management services in partnerships with local authorities. "Parents will benefit because they won't be in a responsive situation," he says.
Parents should modify their environment in advance to make it more healthy, so when the question comes up, they can say that the whole family has been living a healthier lifestyle, and this needs to be built on. Emphasise the entire family's eating and exercise habits and commit to change - but not dramatic ones, says Gately.
Bringing up the weight issue
Is it wrong to broach the issue if a child doesn't bring it up first? The difficulty, says Hill, is if a parent sees it as an issue and wants to raise it. "Judge it - if they don't want to talk about it, don't run the risk of it becoming a contentious issue. If concerns persist, talk to a teacher or [doctor]."
Keep it casual
A parent who feels the need to broach the subject could gently ask a child if they would feel more comfortable if they were in a healthier weight range, says psychologist and writer Amanda Hills. "If they say yes, then offer to help them by cooking more healthy food - but encourage their input as this puts them in control."
The key is to guide and not try to control your child's eating habits, she says.
"Many eating disorders involve the feeling of not being in control," says Hills. "Keep the issue of food casual. Treat it as if it's fuel for a car - don't say that some food is good or some is bad. If a parent does feel the need to point out that something is not the best choice, do it in a low-key way - don't obsess about it."
The key is not letting food become a battleground.
Deflect the issue
"We are hearing of younger and younger children being conscious of their body image," says Mary George of charity Beat. "It's another bit of childhood that is disappearing."
If a youngster brings it up, don't avoid it try but try to deflect it, says George. "Offer praise and encouragement in other areas - tell them they are kind, helpful, happy and generous - steer it away from body image."
Don't make jokes
Parents often don't realise that making a joke about a child's weight can affect them for life, says Hills. "A father, for example, should never call a daughter 'chubby'. A husband shouldn't say negative things about their wife's weight, and vice versa."
Parents must be careful not to be critical of their own weight or that of others, says George. "Even really young children - four- or five-year-olds - will take this on board."
Mum's not on a diet
Research shows that a child is affected by their mother's self-image and the way she treats food, says psychologist and writer Amanda Hills. In the US, this has been referred to as "thinheritance".
"It is absolutely crucial that mum should never say she is on a diet," says Andrew Hill, a body image and behavioural specialist. "All of the people I have dealt with for eating disorders had a mother - or a father - who demonstrated obsessive behaviour around food."
If a mother feels like cutting down, do it in a low-key way, he suggests. "Say something like, 'Mummy's not going to have a big potato because she's finished growing.' But mum should never serve herself a separate meal."
But Andrew Hill says depending on the situation, there might not be a problem with a parent being seen to be managing their weight. "If a parent is going to Weight Watchers, for example, why hide it - it usually means they are overweight and they are trying to manage it."
The key is not to obsess about it, he says.
If a child is concerned about their weight, parents need to create a situation in which children are "active learners", says Andrew Hill, in which they learn from their own mistakes. They need to build self-confidence and self-competence, and parents need to give them the opportunity to go out with their friends and exercise - rather than focusing on their weight, he says.
Set the nutritional agenda
Children consume about 60 to 70% of their food energy at home, so parents set the nutritional agenda, says Hill.
"Older children have more and more liberty and financial power - the key is to get them through adolescence so that they are confident and can make choices about how they prioritise, because later on they will make choices based on their own perception."