My son is 6 now, but I told him some things about drugs probably about a year ago. I told him that drugs can make you do dumb things and they can mess up your body and make you sick. And I told him that some people spend ALL their money on drugs because the drugs makes them not care about anything else. I told him some other stuff too, but I think you get the idea. I told him because he asked my why drugs are bad. And with my son, I tell him things pretty straightforward, but sometimes I have to exxaggerate (sp?) things just a little bit to make them seem SOOOO TERRIBLE that he might think twice before he does something. I try not to leave room for interpretation, cuzz he's so young, and I don't want to confuse him by making him think that even though drugs are 'bad', it's ok to do them sometimes.
I took the same approach to playing in the balls at Chuck E Cheese. I just said, "Reese, you can't play in the balls cuzz they're dirty. Some of the kids poop & pee & throw up in there. And that's nasty." He just said, "Okay Mommy." And the next time we went to Chuck E Cheese, he said, "Mommy, I can't play in the balls cuzz they're dirty, right?" Oh, and I remember when we were there, some little kid found a pair of pliers in the balls. WTF?
So at least I think I make some kind of sense to him.