The following makes more sense if you know what Homeopathy is. The excellent article Darryl Cunningham Investigates: Homeopathy covers the basics in a succinct, comic book format.
This past weekend I had a conversation with my son about quackery. He's 5 and we were buying him more allergy medication. He wanted the package with the colorful cartoon characters on it. They were homeopathic preparations. I started talking to him about what that meant, and at one point he said, "Oh! Fake medicine, like my cheetah is fake!" He was referring to one of his stuffed animals.
I replied with "Kinda, only no one is trying to trick people into thinking your cheetah is real."
I ended up explaining what the "8x" on one package and the "20c" meant on another, and just how dilute that made the original ingredient. It was easy for him to grasp as one of his science kits has a water dropper which he uses to move around small quantities of things. We ended up miming taking one drop of red food coloring and moving it through 8 levels of dilution. When we got to the end he said "But Daddy, there won't be any red LEFT!"
"I think you understand," I said.
In the end he picked the cherry flavored Benadryl. Unfortunately this has reminded him that he does not like the cherry flavor. We've agreed that when this bottle is empty we'll go back to bubble-gum flavor.