If there is a 'face of child obesity', it is six-year-old, 15-stone Dzhambulat Khatokhov. Sheer size has made this boy from a poor Russian family a hero in his home town and an object of fascination in the west. Nick Paton Walsh tracks him down

Just sitting down in Dzhambulat Khatokhov's house sucks you straight into his empty world. "There is not a single piece of furniture that he has not broken," his mother, Nelya, laments as I perch on a stool barely held together by a quiver of nails.

Six-year-old Dzhambulat is 4ft 7in (1.4m) tall but weighs a staggering 15 stone (95kg). Since he was three, he has been touted as the biggest child in the world. But the sparsely furnished flat in which Nelya, 38, lives with the boy-phenomenon known as "Dzhambik" and his superlative-free, skinny brother Mukha, 14, confirms that fame does not always go hand in hand with fortune.

Dzhambik is so big that there isn't room for much else in his life. He is hostage to the attention that his enormousness brings him. People feed him; people talk about how big he is. He takes great pleasure in throwing his weight down on to his only real piece of furniture, a steel-framed bed, grinning as it groans under his weight. At times, he is a walking test of how people view obesity - is he tragically out of control, Benny Hill-funny, or happily rotund? Does he himself know or even care?

You may recognise him: his photograph and proportions are often used to illustrate the increasingly extreme nature of child obesity in the west. Five per cent of British 12-year-olds are clinically obese, and a third of American kids aged between 9 and 11 are considered overweight, with experts predicting that a fifth will be obese by 2010.

Yet beneath Dzhambik's image there is often little more than a brief caption, setting out his dimensions, his gift for wrestling, and the fact that he lives in Kabardino-Balkaria, an impoverished republic in southern Russia.

The story of how Dzhambik (pronounced Jam-Bic) got so big is not a long one, his mother insists. He was born, ate three or four times a day, and just grew. But the life that his size has given him is not so easily summed up. This is a story of an ordinary six-year-old boy stuck in an abnormal skin and a world of adult fascination.

Dzhambik, a local hero, is easy to find. His mother Nelya, 38, agrees to meet me but, two phone calls into our discussions, begins to ask about the "royalties". Other journalists have unsolicitedly paid $500 to meet her son, she says. I explain that the Guardian does not pay for information, then, sensing this is a deal-breaker, add that I might make an exception and pay 5,000 rubles (£100). From then on, all Nelya really wants to talk about by phone is money, trying to get me to agree to twice as much up front.

When I arrive in Terek, an hour's drive from the regional capital of Nalchik, it is obvious why. The town is plush with grass, but little else. Mukha, Dzhambik and his fame are all that Nelya, a nurse and single mother on £60 a month, has. We collect Dzhambik from his nursery school, and my notebook and the photographer's camera immediately plunge us into his world of disproportionate attention.

"Everyone loves him," says his teacher Zhenia Khadinova as his schoolmates bound around him, performing for the camera. "He's sporty, likes singing and English. The kids don't tease him and he is average in class. We can't all be at the top," she adds.

Nelya tells me about a set of tests that Dzhambik had done in Moscow two years ago, which said that he was healthy. "It said his organs were of proportionate size," she says. "He's only been ill with flu once. He eats three times a day, sometimes four. He was born a normal 6lb 6oz."

We should mention at this point that Dzhambik, who most of the time looks at the floor, is really very fat indeed. His eyelashes are forced upwards by the rolls of fat that are his eyelids. His thigh fat hangs over his knees. His wrists look as if they have been swollen by bee stings. When he walks down the stone staircase inside the school, it thuds.

He is not much of a talker, and we try to escape the crowd in the local park. He sits down on a bench, his brother's friends still milling around. "He's not a local hero, but an international one," says Murat, 14, before confiding that his nickname in school is "Boba," or Gladiator. I ask questions, about school, sport, his size. What I get is a few words of schoolboy English: "My name is Dzhambik." "I like to be big," he eventually adds, with a little help from Nelya.

During our two afternoons together I am run through the gamut of things he "does" for the camera. He sings something Nelya says is a version of the alphabet. He puts his arms in a Popeye pose. He stands on the scales, his arms perfectly straight down each side, as if standing to attention. He hulas a large metal hoop. He puts on a jumbo-sized wrestling vest and fights with his brother, occasionally thumping him with such force that there is a significant pause between Mukha being hit and Mukha laughing, during which Mukha wonders whether someone eight years his junior should be getting away with this.

Yet Dzhambik seems truly happy when we play draughts on a chessboard I have brought him. "I'm going to beat you," he laughs, thumping his palm on the carpet before letting out an enormous belch.

The absence of furniture means we are both lying on the floor. Dzhambik does not so much lie down as bellyflop on to the carpet. His huge stomach means he can't stand up normally by bending his knees. Instead, he must get into the start position for a press-up, and slowly edge his hands and feet closer together until he can balance and bend his back upright. It is as if his limbs are held straight by plastercasts of fat.

Around him are the trappings of his childhood: the photographs with Russian chatshow hosts, the encyclopaedia he reads from, and a certificate from a Russian organisation that registered his apparent world record. Aged three years and two months, he weighed 6st 3lb and was "the biggest child in the world", considered "perfectly healthy with unique strength". The certificate claims affiliation with the Guinness Book of Records, but a Guinness spokesman said they had no record of Dzhambik and were unlikely to have a "biggest child" category. All the same, Dzhambik is way ahead of his two competitors across the border in Georgia, three-year-old Luka Meliksishvili, who weighed 4st (26kg) when he was only 15 months old but is reportedly growing by 4lb or 5lb (2kg) a month, and Georgiy Bibilauri, who was 9st 8lb (62kg) when he was five.

Dzhambik doesn't like losing at draughts, and is more than a handful when unhappy. As Nelya changes him out of his wrestling vest and puts on his Ronaldinho football shirt, he grumpily decides to thump her a couple of times. Nelya tries to laugh it off. She holds up his size 58 shorts and says, simply: "Nightmare." She asks me, concerned: "Do you think a child like this has any future prospects? Might some British TV producers be interested in him?" Dzhambik is clearly tired, and I leave.

We meet up again the next day at the Vostok entertainment arcade. Dzhambik loves the video games hall; the video games hall loves Dzhambik. As her two children drive racing-car simulators imported from Japan, surrounded by goggle-eyed kids, Nelya tells me: "He does not eat that much." Then she adds: "He is happy that size. It is not shameful. He likes showing people how strong he is."

She says such huge people are native to Kabardino-Balkaria, a sleepy collection of spa towns and idyllic greenery in the north Caucasus, a two-hour drive west of Chechnya. The predominantly Muslim republic, one of Russia's poorest, saw a violent uprising in the capital, Nalchik, last October, when police buildings were attacked by hundreds of local men, part of an Islamic underground formed in response to police brutality and corruption. Yet Dzhambik's hometown of Terek seems a million miles away, a place of legend and tradition. Nelya refers to "Sosruka", a Kabardinian legend about a friendly giant born in a village. In a region where wrestling is a popular sport, Dzhambik's size is easily cast as an athletic advantage.

Nelya says that Dzhambik and Mukha, who are the same height but 9st 4lb and eight years apart, have different fathers. Mukha's dad, also father to her 18-year-old son Rezuan, who is currently serving as a conscript on Russia's border with China, is not around any more. Dzhambik's father, Mikhail, 40, a taxi driver, lived with Nelya for five years, but left shortly after Dzhambik's birth. He visits perhaps twice a month, she explains. "His ancestors were very big," she says. "Mikhail was born in a triplet and we say that the size of his two siblings and ancestors went into Dzhambik."

She says that when he was a month old, Dzhambik began to grow at twice the usual pace. "After one year he weighed 2st 7lb and began to walk without any problems, and talk, too. He always liked lifting things and sport."

She says the record organisation contacted them during their first trip to Moscow in 2003, after which Dzhambik's weight hit the front page of Russia's biggest selling paper, Komsomolskaya Pravda. They travelled to Ukraine, Georgia, Tokyo, Moscow, France, Germany and the Czech Republic as Dzhambik's fame spread.

She looks lovingly at both her kids. "One day they will both be Olympic champions and look after me," she says. "We're moving to Nalchik so Dzhambik can have a professional trainer and learn to swim. The doctors say he is a truly unique child. His psychology is already that of an adult. He sorts out situations like an adult does."

Dzhambik has run out of game tokens and comes over to me. After irritably throwing some toys onto the table where we are sitting, he says: "Nick, play cars with me!"

Soon, cars turn into ice cream. I buy the boys an ice cream each. As we sit outside the video games hall, Dzhambik demolishes and grabs Mukha's. Neither Mukha or Nelya notice. A passerby asks if she can have her photo taken with Dzhambik.

As the boys get restless, we move to a nearby fairground, where Dzhambik soon becomes the main attraction. The fairground owner grants us a free pass to all rides, an act of generosity soon explained by the crowd that follows Dzhambik around, wanting to have their pictures taken with him. Nelya sighs: "See how everyone comes up to him. He is exhausted by that." Each time the shutter closes, his face softens to offer a perfect smile, a pose clearly practised over years. We sit in the cafe for a few minutes before another crowd gathers for a photo opportunity. Some of our neighbours are angry at having their space invaded.

Dzhambik loves the dodgems and raises his middle finger at me when he crashes into me during one race. After his fourth free go, we move back into town for a proper meal.

The waitresses at the cafe want their picture taken with him, too. The man at the next table asks if he can buy him an ice cream. "See how people act with us," says Nelya. "That is how it is for us." I ask if Dzhambik, now on his fourth ice cream in as many hours, could perhaps eat less. "He does not always eat this much," she replies, a little embarrassed. He finishes his ice cream and grabs a piece of bread. "Stop," says Nelya, and he puts the bread down.

It must be a complicated relationship, Dzambik and food. It has brought him his fame, and if he stops eating so much, then he will spend the rest of his life as the man who used to be the fattest kid in the world. Nelya doesn't talk much about how his life will be if he keeps these proportions when he is older, but seems sure his health is fine.

Back at home in Terek, she shows me the two medical analyses done by Moscow doctors. Dr Sergei Podulov, who examined him once in 2003 and once in 2004, said: "Dzhambik is absolutely healthy. He has no illnesses." He said Dzhambik's grandfather was also a "Bogatyr", a Russian word for a sort of gentle giant. Both the medical analyses end with the recommendation that he should wrestle and do sumo for exercise.

Today, Nelya lacks the means to investigate Dzhambik's situation further in the costly and sometimes unscrupulous world of Russian healthcare. "Why test him all the time if he is healthy?" she says. "It's expensive to fly to Moscow and the blood tests are traumatic for him."

At home again, the kids are captivated by a new musical system the magnanimous Guardian has bought them (£40). I ask Dzhambik to list his favourite things. "The music system," he says. "Your watch (£20, now on his wrist). And money." He buries his face in Nelya's arm and giggles. When I later give Nelya 8,000 rubles (£160), she looks at me and asks: "I don't want this if it comes out of your pocket, understand? Only if it is the Guardian's." She asks me to hand it to her discreetly. "I don't want the children to know where it comes from," she says.

As I turn to leave and they return to being a normal family again, the emptiness of the flat looms. Nelya, her face reddened by the spring sun and wrinkled by the exhaustion of being Dzhambik's main connection to the outside world, follows me down the stairs outside. She says, pleadingly: "Please do not write anything bad about us."