I was going to title this post, "Depressing News of the Day", because that's what this finding is for me. There is an alarming increase in overweight/obesity for preschoolers on a global scale. This increase is now happening in both developed and developing countries, and across all racial groups.
The paper doesn't really go into the causes except to say that is likely due to changes in nutrition and physical activity. They do point out that this is a dire problem given its future implications:
"Intrauterine, infant, and preschool periods are considered possible critical periods for programming long-term regulation of energy balance (22–24). Waiting for school programs to address this problem is probably too late."