[Aliantha]

Here's one that used to work when my kids were little, but doesn't work so well now.

They used to wonder how I knew when they were fibbing. Of course the real answer is that parents always know because of the transparent body language. Little kids of course don't understand this concept, so I just told mine they got a red dot on their forehead when they were fibbing. This made my life much more amusing when son number 1 started putting a hat on if he was trying to put one over me.