The behavior of eating goes well beyond eating what you think is "good" for you. The most common thread in all of my work with clients, no matter what their eating problem, is that eating (or choosing not to eat) is many times used to calm and comfort. This is true for all ages.
Please remember this when you talk to your kids about eating and weight. As a nation, we are doing a much better job of addressing the need for our kids to become more active and have access to healthier foods, but we are leaving out a major issue-emotional health.
http://www.nlm.nih.gov/medlineplus/videos/news/bullying_weight_041911.html