It is a combination that she says is "deadly." 'Kids should get 60 minutes of exercise a day' What's more alarming is the pervasiveness of the problem among the world's youth. From the WHO report: Childhood obesity is one of the most serious public health challenges of the 21st century. The problem is global and is steadily affecting many low- and middle-income countries, particularly in urban settings. The prevalence has increased at an alarming rate. Globally, in 2010 the number of overweight children under the age of five, is estimated to be over 42 million. Close to 35 million of these are living in developing countries.