Between 1975 and 2016 the estimated number of obese boys in the world increased from 6m to 74m.
Girls showed a similar trend, with their obesity figure rising from 5m to 50m over the same period.
Much of the increase in recent years has taken place in developing countries. Obesity rates among young people in Europe and the US were said to have plateaued.
Despite the trend, more children around the world are severely underweight than overweight, the research showed.
Overall, the global prevalence of child and adolescent obesity had increased from 0.7% to 5.6% for girls, and from 0.9% to 7.8% for boys. Current childhood obesity rates were highest in some Polynesian islands, where they exceeded 30%.
A fifth of children and teenagers in the US and a tenth of those in Britain were obese.
In total, 124m children and adolescents around the world had a body mass index (BMI) of 30 or higher, categorising them as obese.
A further 213m fell into the “overweight” range, with BMIs of between 25 and 29.9. BMI is a standard measurement that relates weight and height.
The researchers pooled together 2,416 studies looking at BMI and obesity to analyse data on 128.9m participants from around the world, including 31.5m children and teenagers aged five to 19.
The results appear in The Lancet medical journal ahead of World Obesity Day today.
Professor Majid Ezzati, a member of the team from Imperial College London, said: “While there have been some initiatives led by governments, communities or schools to increase awareness about childhood and adolescent obesity, most high-income countries have been reluctant to use taxes and industry regulations to change eating and drinking behaviours to tackle child obesity.
“Most importantly, very few policies and programmes attempt to make healthy foods such as whole grains and fresh fruits and vegetables affordable to poor families.
“Unaffordability of healthy food options to the poor can lead to social inequalities in obesity and limit how much we can reduce its burden.”
Leanne Riley, a study author from the World Health Organisation, said: “The trends show that without serious, concerted action to address obesity ... the health of millions of people will be needlessly placed in great jeopardy.”
The research also showed that around the world 75m girls and 117m boys were moderately or severely underweight in 2016. Almost two-thirds of underweight children lived in southern Asia.