Heart failure, caused by obesity, has killed a child aged just three, it has been revealed.
The shocking case was highlighted in a scathing report on obesity by MPs which says too little has been done to tackle the epidemic.
The case was revealed by doctors at the Royal London Hospital.
Specialists there have also seen four children "choked by their fat" who need breathing assistance to treat sleep disorders caused by blocked airways.
The Commons Health Committee warned that obese children could become the first generation to die before their parents.
The report warns obesity has grown by almost 400% in 25 years, with three-quarters of adults now overweight or obese.
England has the fastest growing obesity problem in Europe, with childhood obesity tripling in 20 years.
Dr Sheila McKenzie, a consultant paediatrician at the Royal London, told the Health Select Committee: "In the past two years one child at the age of three has died of heart failure secondary to extreme obesity."
She said the four cases of sleep apnoea that she had seen could be indicative of further cases.
The condition occurs when the airways become blocked by folds of fat.
"In other words, they are being choked by their own fat," she added.
"Were we able to study all severely obese children, I am confident we would identify many more with obstructive sleep apnoea."
The Daily Mail reported that the three-year-old who died of heart failure was a Bengali girl from east London who should have weighed around 2st 4lb (14.5kg), but instead had a Body Mass Index
(BMI) which equated to around 6st (38kg).
BMI is calculated by dividing weight in kilograms by the square of your height in metres.
Dr Nigel Meadows, a consultant paediatrician at the Royal London Hospital, told the newspaper: "It was a shocking case.
"You don't imagine your kid is just going to die of obesity. The parents were devastated.
"Some may say the parents are responsible, but if a child is demanding food it can be very difficult to refuse it."
Doctors at the hospital also reported many young patients had abnormally high insulin levels, an indicator for Type 2 diabetes, which is related to obesity.
Dr Tim Barrett, of Birmingham Children's Hospital, told the BBC: "Our clinics are currently being flooded out with overweight children.
"At the moment, we haven't got adequate treatments at all. We need to set up specialist clinics for them."
David Hinchliffe, chairman of the committee, said: "We were all shocked when we heard about the young girl.
"I see in my constituency children who are grossly obese, but to hear of a girl dying from heart failure was shocking."
He added: "It was the first situation of its kind we had come across but we feel it may become a more serious consequence of obesity in the future."
The committee's report attacked the government, NHS, the food industry and advertisers for failing to do enough to address the growing problem of obesity.
It made almost 70 recommendations about what should be done, focussing on the importance of ensuring children eat well and learn about nutrition.
It also called for a voluntary industry ban on junk food ads to children, warning a statutory ban should be introduced if that failed.