I agree that obesity is not largely about whole grains and vegetables, it's about terrifically bad parenting, eating habits, all coming down to caloric intake.
Second, having more whole grains and healthier food (no trans fat, a balance of protein, fiber, carbs, good fats, whole foods) is also a no-brainer.
That kids turn their noses up to it..of course, that's not what they were raised on. That's a parent/culture issue.
Both are issues. However someone notes correctly above that a few generations back it was largely less or unprocessed foods...what we're trying to go BACK to...so claiming it's ONLY about portion does appear to miss that too.