But, some experts suggest that we've merely saturated the field of those predisposed to become obese at a young age. Here is a snippet, but you can read the whole piece here.
If, at 17 percent, we've hit the "saturation" point for child obesity, we're extremely lucky. There's no historical basis for knowing where the saturation point is, since our species has never before lived in an environment so full of ease and abundance. The far more dangerous possibility is that the saturation point is higher. In fact, given that we evolved in conditions of scarcity, it's logical to suspect that the tendency to seek and store fat is nearly universal. As the Los Angeles Times observes, "the idea that childhood weights have simply topped out doesn't quite square ... [One expert] said the fact that 60% of U.S. adults were either overweight or obese suggested that children had plenty of room to grow."