China’s little emperors are not so little anymore. A new study shows that childhood obesity rates in some parts of rural China have skyrocketed, leading to what authors say is a “serious” public health problem. In rural Shandong province, the percentage of overweight and obese boys jumped 60-fold, from just 0.5% in 1985 to 30.7% in 2014; in girls, those rates rose from 0.8% to 20.6% over the same period, the authors report online today in the European Journal of Preventive Cardiology. Why the sudden increase? Researchers say a nationwide shift to high-energy Western diets—including fast foods and soda—combined with more time behind computer and television monitors underlie the trend. But that’s only part of the story: As average household incomes have risen dramatically across China, many previously poor families are overfeeding their only children (this is especially true when grandparents are in charge). Compared with the country as a whole, the new numbers are high—an international survey by The Lancet in 2014 found that just 23% of boys and 14% of girls in all of China were obese or overweight. That discrepancy could stem from smaller sample sizes or other unexplored factors, says epidemiologist and health economist Eric Feigl-Ding of Harvard University, who was not involved in the study. But the bottom line remains the same: China’s littlest citizens are growing up—and out—quickly.