I think the key is in allowing children to have unhealthy foods in moderation. I had a friend in middle school who was not allowed to eat any junk food or fast food. When she was away from her parents she would binge -- completely out of control -- on any sugar she could get her hands on, which often made her sick. It's critical to teach kids healthy habits from a young age so that they can make responsible decisions for themselves as they grow older and as parents have less control over what they do. I think that by placing junk food in a "forbidden" zone, parents only teach their kids to want it more. Junk food in moderation or as a special treat is fine.