I also know that PSAs that sugar-coat things don't tend to work, especially on kids. Consider the Truth ads. These have been very successful, in large part because they are honest. (Of course, they are not funded by big tobacco. And you will notice you see fewer of these because the organization lacks the money power of huge corporations.)
However, I wonder why there are not more PSAs aimed at people to encourage them to be more encouraging. Not “positive.” Encouraging.
I have been helped a great deal by the little bits of encouragement throughout the week. Lots of people will tell me very specific, but thoughtful things, and those help me to keep in mind that my diet and exercise are working. What doesn’t help? Advice. Most of it is something I already know. Some of it comes from the perpetually skinny and is over simplistic. What also hurts are those who think they are encouraging by telling me I’m still fat. One relative will hear another talk about my weight loss and say "Really? It looks like you have gained weight" or "I can't tell" or "Well, it's about time you did something."
I have a long way to go, and I know it. I'm fat, and I know it. I didn't get the weight on quick, and if I want to live a healthy remainder of my life, I can't get it off fast. I just also know that there is, at least for me, an emotional attachment to food as well as to sitting still. And having people honest and thoughtful has made a huge difference in how I handle the really difficult parts of the weight loss journey.
And while we are at it, why not some PSAs aimed not just at the parents who raise fat kids, but at the executives of fast food industries and the government autocrats who protect them. These are people who on one hand block every attempt at health care reform and on the other block attempts to make food healthier and safer. These are people who seem all about the money, but ignore the economic realities of the products, policies, and practices. But such efforts would not likely work. Most PSAs appeal to the heart, and these people don't have any.