This deceptively cute video (5min) illustrates how addiction works. If you are a parent, teacher, counselor or spiritual leader take a moment to watch the video and think about the kids it would work for. I think it can act as a powerful teaching tool for kids 4 to 10 yrs old.
I would recommend if you show it to the kids in your life that you use an inductive approach. Ask them open-ended questions like: "what happened when the bird first tried the nugget? what about the 2nd and 3rd time? what happened at the end?"
Then, once the kids describe it all, ask them how it made them feel? Then, you can talk about how there are things in the world that can bring great "darkness" into their lives. In age appropriate ways I would list what those things could be. "A nugget could be an image on the internet, something you drink, something you smoke..."
So, when do you think you will show this to your kids? Set a time now while you are thinking about it. It could make a huge difference.