Across the developed world, life expectancy has risen consistently since the 1930s - yet our children's health is a 'ticking time bomb', experts warn.
Youngsters will be less healthy than today's 65 year olds by the time they reach that age, new research claims.
The warning comes as the latest NHS figures reveal one in every five children aged 10 to 11 is obese.
Lifestyle-related problems such as consuming too much sugar and doing too little exercise are already causing health problems among children, the researchers say.
The Economist Intelligence Unit, who directed the research, are calling for action to tackle the crisis.
'Considering the longer life years that today's children can expect, it makes sense to focus on health practices that will increase the chances of making those longer life years healthy ones,' the unit's research director Aviva Freudmann said.
Today's youngsters will be less healthy than our adults by the time they reach the age of 65
A QUARTER OF TEENS EAT SWEETS EVERY DAY
A World Health Organization (WHO) report released this month revealed a 'bleak picture' of young people eating and drinking too much sugar and spending too much time sitting down.
One quarter of adolescents in England and Wales eat sweets or chocolates every day, the report claims.
It also showed that 14 per cent of teenagers have a cola or similarly sugary drink every day.
Even more teenagers in Scotland have a sweet tooth, with a third eating some sort of confectionery and 23 per cent consuming a soft drink daily, the report adds.
And across Europe, adolescents spend 60 per cent of their time sitting down.
Gauden Galea, director of the WHO's division of non-communicable diseases, which includes obesity, described the findings as 'a bleak picture'.
He added: 'Most young people will not outgrow obesity: about four in every five adolescents who become obese will continue to have weight problems as adults.'
The report is based in part on a survey of educators in five countries - Germany, South Africa, India, Brazil and Saudi Arabia - and focuses on the health education of children.
Of 101 polled educators, 58 per cent said children can expect worse future health than today's older adults.
The educators identified sedentary lifestyles, being overweight and poor hygiene as the main health problems children face that may lead to later problems.
Recent research by King's College London found that children who are obese have four times the risk of developing type 2 diabetes.
And Simon Stevens, head of NHS England, has noted more than once that while a quarter of children entering primary school are overweight or obese, the proportion rises to a third by the time they leave.
The controversial 'sugar tax' that will come into force next year will be 'good news for our children', according to Chancellor of the Exchequer Philip Hammond.
Oxford University experts agree, saying the tax will have a significant impact on tackling child obesity in a study last December.
Professor Richard Tiffin from the University of Reading, who was also involved in the aforementioned study, said: 'Childhood obesity is a ticking time bomb and we must now turn our attention to other measures that will bring about the step change in diet that is necessary to truly tackle this issue.'
The growing problem has led to calls for the Government to take tougher action to tackle childhood obesity.
Theresa May's obesity strategy has been criticised over its failure to impose junk food advertising restrictions and its reliance on voluntary action by the food and drink industry.
Campaigners argue that Downing Street caved in to pressure from the food industry by not enforcing mandatory reformulation of food to reduce fat, salt and sugar.
Adverts for junk food are already banned from children's television, but campaigners have argued the existing ban is insufficient.
Labour has said it would ban adverts for junk food and sweets appearing before the watershed in an attempt to tackle childhood obesity.
The policy echoes demands made by TV chef Jamie Oliver, who campaigned for such a ban.
Without these measures, the NHS will come under 'enormous and unsustainable strain' from a condition that already costs £5bn a year, the Obesity Health Alliance argues.