overweight and underweight babies

It's said that one in three children in the U.S. are overweight. One family has a baby who was less than five pounds after birth, and then 3 years later, weighs 43 pounds. I'm assuming this family isn't the only one who is suffering. Something is terribly wrong though. Are pregnant mothers eating too much chocolate? Are they forgetting about their own baby's health? If the mother is gaining too much weight, depressed, smokes, or has diabetes, then that might be a good explanation as to why their child isn't 'normal'. It's sad. :(