Our family, influenced by me mostly, refrains from caffeine and alcohol as part of how we observe the Word of Wisdom. I interpret it as any addictive substance. If it is addictive, we simply stay away from it. I may joke about being addicted to chocolate, or reading, but am not truly addicted to anything... the Internet may be a close addiction. Anyway - the point is, they are well-versed in what not to drink, eat, etc...
We've also taught them that just because we don't subscribe to certain foods or drink, that doesn't mean other people don't. We've taught them that people will choose to smoke, drink, and do other things because it makes them feel good. It isn't necessarily healthy or wise, but they do it because those things can bring momentary pleasure. Part of our life is about having moral agency to choose.
So my girls were heartbroken that Daddy had drank three sips of the diet coke to celebrate with the rest of his drinking co-workers on that great sales day.
We told our daughters that they were correct in their choices. Daddy promised he wouldn't do it again. I explained that even Daddy makes mistakes. I like it when they see that we aren't perfect - because we so aren't. There's something utterly devastating about growing up and realizing your parents aren't perfect, but pretend to be. These girls of mine are such good, wise girls when it comes to doing the right thing. They are, in many ways greater than us. I knew this when they were growing in my womb.
When we left, my husband found this written on his white board.