Children born since 1990 are up to three times more likely than older generations to be overweight or obese by the age of 10, a study has found.
Researchers at University College London (UCL) said children were also becoming overweight or obese at an increasingly younger age.
The trend is increasing the risk of developing chronic health conditions such as coronary heart disease and type 2 diabetes, they warned.
"In the absence of effective intervention, overweight and obesity will have severe public health consequences in decades to come," the study, which is published in the American journal, PLOS Medicine, concluded.
The obesity epidemic is projected to cost the NHS £22.9 billion a year by 2050, the authors said.
Nearly two-thirds (64%) of adults were classed as obese last year, according to Public Health England (PHE).
Latest figures also show that a third of 10 to 11-year-olds and more than a fifth of four to five-year-olds were overweight or obese.
The large-scale study saw teams analyse the body mass index (BMI) of more than 56,600 participants in the UK born between 1946 and 2001.
Obesity is commonly defined as a body mass index (BMI) of 30 or more, while people with a BMI of 25 or more are considered overweight.
While the average age that males who were born in 1946 entered the overweight range was 41, it went down to 33 in 1958 and by 1970, the average age that men became obese was 30.
Women born in 1946 who became obese did so at an average age of 48, while for those born in 1958 it was 44 and 41 for those born in 1970.
The study authors said the tendency of people with greater BMIs to under-report their weight suggests the results are conservative, if anything.
"Many more children are overweight or obese than in previous generations and, if the observed trends in adulthood BMI continue, the majority of children are likely to develop overweight or obesity at some point in their lives and at younger ages than did previous generations," they warned.
They added that understanding the characteristics of those who maintain a healthy BMI throughout their lives may help clinicians in dealing with overweight patients.
Co-author Professor Rebecca Hardy, of UCL, said: "The more of their lives people spend overweight or obese, the greater their risk of developing chronic health conditions such as coronary heart disease, type 2 diabetes, high blood pressure and arthritis.
"While other research has shown that losing weight at any point in adulthood can help reduce the risk, this study indicates that the UK needs to target its public health interventions at younger and younger ages in order to stem the spread of the obesity epidemic."
The project was carried out as part of the collaborative research programme Cohorts and Longitudinal Studies Enhancement Resources (CLOSER).