American childhood obesity – what’s going on?

You may remember headlines at the end of February such as "Obesity Rate for Young Children Plummets 43% in a Decade" and "New Jama study: US toddler obesity rate plummets", as reported by the BBC.
These headlines came from a study called "Prevalence of Childhood and Adult Obesity in the United States, 2011-2012" (February 26th 2014).
The February Study
The February report  was based on a sample si...