Childhood obesity in the United States has tripled in a generation. But while debates continue over the content of school lunches and the dangers of fast food, we are just beginning to recognize the full extent of the long-term physical, psychological, and social problems that overweight children will endure throughout their lives. Most dramatically, children today have a shorter life expectancy than their parents, something never before seen in the course of human history. They will face more chronic illnesses such as heart disease and diabetes that will further burden our healthcare system....