This is a story I found via Yahoo! on ABC News. I find it hard to believe. I wonder what other countries they included in the survey. Reasons given were: worse health care for children in the US, and too much junk food which give too much growth hormones too early on. Neither of these is particularly compelling to me. I remain somewhat skeptical about whether they included all that many countries in the survey, and whether the reasons offered up are the correct ones. Here's the link to the video. The kid's reaction at 1min54 seconds is hilarious.
Update: A reader alerted me to the actual paper where this information is published. This seems to be a much more complicated story than what the news story describes.