The WHO has warned that the number obese and overweight children in the world could shoot up from 44 million (2012) to 75 million (2025).
This is faster than the growth rate from 1990, when the number was 31 million, said the UN's health body.
In Africa alone, the number of obese and overweight children expanded from four to 10 million over the same period.
"Child obesity is one of the major health issue for tomorrow and today," Peter Gluckman, who co-presides over the Commission on Ending Childhood Obesity, told reporters in Geneva.
The 15-member commission was created by the WHO in June and finished its first meeting on Friday.
Overweight children are more likely to develop serious diseases like diabetes or cancer, and action now may prevent a heavy burden on health systems in the future, said Gluckman.
"Social scientists, public health specialists, clinical scientists and economists will join together to synthesise the best available evidence into a coherent plan," said a WHO document on the commission's mission.
It must produce a report for the World Health Assembly, the decision-making body of the WHO, which meets in Geneva once a year.