Jusna Begum lives near the South Bank in London with her four children, aged between one and 11. When a health visitor told her that her three-year-old girl was “on the chubby side”, Begum was surprised. “I didn’t think she was at all; I had felt like my children weren’t eating enough.”

She did, however, accept an invitation to join a six-week healthy parenting programme called Henry. Four weeks in, she has rebooted her family’s lifestyle, from making dinner times earlier to allow for more activity before bed to the food she prepares. Coming from an Asian background, says Begum, “There’s a lot of fatty food – we use a lot of oil and salt in curries.” Her children also loved drinking juice and snacking on crisps and chocolate after school. “I would just allow them,” she says, incredulously. “I thought it was normal.”

In following her health visitor’s advice, however, Begum is in a minority. Just one-third of parents who are informed that their child is overweight or obese accept any help offered to them. Peymané Adab, a professor of chronic disease epidemiology and public health at the University of Birmingham, has been developing obesity prevention and management programmes for nearly 20 years, including studying parental responses. “There is definitely underrecognition of obesity,” she says. “Part of it is that we base our judgment on what’s normal, what’s around us, and as more children become obese and overweight you compare and say: ‘My child isn’t that overweight.’”

In the 1980s, less than 2% of those aged five to 10 were obese. These days, one-third of children are overweight or obese by the time they leave primary school, yet many adults don’t see the problem. A 2014 study in the British Journal of General Practice found that parents don’t tend to class their children as overweight until they are in the 99.7th centile, which is morbidly obese.

“Some parents don’t think children can be overweight,” says Adab. “They talk about puppy fat, and they think the children will grow out of it. They don’t see it as something that becomes established – and yet the evidence is that it does track through [into adulthood].”

While every child develops differently, healthy puppy fat generally ends with toddlerhood. The critical periods are around ages five and six and again around puberty when, says Adab, there is a tendency for weight gain and “perhaps we should be intervening more”.

Cooking together can help make healthy habits fun. Photograph: Halfpoint/Getty Images/iStockphoto

From age three and up, the main way parents are informed that their children are overweight is through the National Child Measurement Programme (NCMP), which registers children’s body mass index (BMI), once at four or five and again at 10 or 11. But BMI, a calculation based on weight and height, has limitations – for instance, it underestimates body fat in south Asian children (the demographic with the highest levels of childhood obesity) and overestimates it in black children.

Another problem with the NCMP is there is no hard and fast procedure on informing parents of the result – it was set up to monitor trends, not as a screening strategy. “Some local authorities contact families of the children who were overweight and try to get them to engage in services; some don’t do anything other than send a letter,” says Adab. “We don’t know what the best approach is.” Many simply don’t trust the figures. “Even colleagues here, working in academia, have said they’ve binned that letter because they think it’s rubbish.”

Attempts have been made to word the notification differently, to little effect. “It’s an impenetrable problem,” says Adab – and it is exacerbated by our sugar-coated and deep-fried food culture. Her daughter was given chocolate by teachers as a reward. “I was part of our parent-teacher group and remember trying to speak up, saying maybe we shouldn’t have so many sweets,” she recalls. “All the parents thought I was from another planet.”

At least in primary school, there is some control over what children eat; the newfound autonomy of starting secondary school – and the sweet shops and fried chicken joints that come with it – poses the greatest challenge. Taste preferences are formed in early life: even exposure to flavours in the womb influences later habits, while sugar – separate to weight gain – conditions our brains to crave ever-bigger sweet fixes. “From a young age we can start getting children used to less sugar and less fat,” says Dr Angela Donin of the Population Health Research Institute at St George’s, University of London. “If they’re more used to snacking on savoury crackers that are high in oats or bran, and fruit and nuts, that will hopefully shape their preferences.”

Donin’s research has found that having a large breakfast every day, particularly a high-fibre cereal, is associated with lower adiposity. But swapping that in for sugary cereals can be difficult, not least because even plain old bran flakes are usually at least 10% sugar – you still have to read the labels.

Presentation works wonders. Photograph: ThitareeSarmkasat/Getty Images/iStockphoto

“It is very difficult, once taste preferences have been formed, to try to change those as a parent, but take small steps to start with and try to ensure your child has a high-fibre breakfast every day with reduced sugar,” says Donin. “Make sure they’re having enough sleep, cut back on those sugary drinks and free sugars [added sugars and those in honey, syrup and fruit juice], and think about healthy snacks that will increase their fibre and micronutrient intake.”

In 2017 Zoe Willman, who lives in Sheffield, sought help to persuade her two young sons, who have autism, to eat anything other than chicken nuggets and potato faces. “My eldest would eat cucumber, but apart from that vegetables were a no-go, and I was really worried they weren’t getting what they needed.” After a year working with a Henry volunteer, “Now we’re on fish,” she says proudly. Simple changes such as making shapes out of food and reward charts for trying something new have worked wonders. A healthier diet seems to have changed Willman’s children’s behaviour for the better – “There are more calm moments now” – and she herself has shed several stones.

Begum was also pleasantly surprised by the Henry programme’s help in introducing healthy snacks to her family. She says it taught her simple presentation tactics, such as making carrot sticks, which are pleasing to children’s palates. “I peel and slice apples and then they’ll eat them. They love carrot and cucumber sticks with hummus now. Giving them a packet of crisps is easier than having to peel and cut fruit, but my kids really love it – and vegetables. It is expensive to buy, rather than the fatty stuff, so I’m careful not to waste it, freezing vegetable portions for dinners.”

For parents who are anxious about their children becoming obese, the temptation can be to restrict certain foods and stress the terrible consequences of eating them – but this approach comes with its own concerns about instilling complexes. “It is a difficult balance, but I don’t think we should be saying there are taboo foods that we shouldn’t have,” says Adab. “That extreme has definitely been shown to lead to problems. It’s fine to have sweets on occasion but it should be no more than once a week. Every day we drink water rather than fizzy drinks.” But this isn’t easy, she says, and there needs to be a bigger buy-in from schools and parents. “If it became the norm it would be different.”

Given the temptation-laden world we inhabit, will trying to limit access to unhealthy snacks encourage children to binge on them when they get the opportunity? Adab says there isn’t a scientific consensus as to whether restriction leads to weight gain. “Some studies do find an association, but we recently completed a study and found there isn’t an association when you adjust for children’s weight at the start. It could be that parents are restricting because their child is overweight, rather than the restricting causing the weight.”

Eating together around a table is important. Photograph: Monkey Business Images/Getty Images/iStockphoto

Zeroing in on weight and size, however, is psychologically unhelpful. Many professionals now emphasise positive, healthy living. “There is very little evidence that weight management programmes lead to unhealthy behaviours,” says Adab, “but there is always a concern that children will slip into eating disorders. It is still an area that is underresearched, but on the whole most weight management programmes don’t result in unhealthy behaviour if they are done properly.”

The trend now is for weight management programmes to call themselves healthy lifestyle programmes, incorporating increased activity, prioritised sleep and limited time on devices into daily routines. “Providing hands-on activities rather than didactic stuff improves uptake and retention,” says Adab. Donin says that the Child Heart and Health Study in England (Chase) of about 5,000 children aged nine to 10 found lower screen time was linked with a lower fat mass index.

Stephanie Byrne, a Henry practitioner who works in Lambeth, south London, says she tends not to mention weight at all: “It’s more about looking at the whole lifestyle of the family and getting people to identify where they want to make changes.” Rather than going on a diet, families might decide to buy a dining table. “We talk about eating slowly with other people, regular meals, portion size, not snacking all the time, turning the TV off, talking to children and giving them lots of praise and rewards. The evidence shows that is the best way to tackle childhood obesity and being overweight.”

Begum has picked up ideas for how to make being healthy fun, from involving the children in cooking to creating a lucky-dip jar of activity options. “I’ve seen the difference in the kids,” she says. “I used to struggle to get them to bed but now they get tired. Before, I just didn’t think about healthiness.”