'I heard somewhere that kids, if left to their own nutritional urges, will quickly gravitate toward foods that are actually beneficial to their own nutrition.'
Really? If this is true, then that is really quite a profound discovery which brings with it many implications. It might be the case that the young mind only seeks out 'unhealthy' food simply because they're told it's bad, and so they see it as an exciting treat (unless they have developed a morbid sugar addiction).
It would also look good for child/adult relationships. I have heard other people say here and elsewhere that children tend to gravitate toward child-lovers because they can sense the loving (emotionally nutritious) goodness that we want to endow. Perhaps society underestimates the instincts of the child.