Since the girls have been old enough to climb into normal sized chairs, we have been pretty consistent in enforcing the "sit down" rule. That is: No standing, jumping, or otherwise playing on chairs.
We enforce this rule with two phrases: "Sit down, please", and "Sit down . . . on your butt!"
The second phrase is often used because the girls like to squat in their chairs pretending to sit, but will then use the opportunity to spring in the air like a jumping jack. (Of course in their minds, Mommy or Daddy will always be there to catch them before they crash to the ground!)
So tonight before bed we were reading their favorite books before bedtime, and for the thousandth time, we read their Curious George book, which has this photo on the last page:
Upon seeing this photo, my girls, for the first time, cried out: "Monkey! Sit down . . . on your butt!"
At least I know they've been listening to me all this time.