There's no better way to introduce preschoolers to Kant's
moral imperative than Jo Ann Stover's
If Everybody Did, an entertaining romp through the consequences of every person in the room engaging in the same minor misbehaviors after one child does a demo round. We have a love/hate relationship with morally instructive children's books, but we are learning over time that what makes them work well in our household is humor. From Jane Yolen's
How Do Dinosaurs Eat Their Food? to Maurice Sendak and Sesyle Johnson's
What Do You Say, Dear?, the use of humor puts everyone at ease while gently introducing real concepts that need teaching - in this case, helping kids conceive of the consequences of what would happen "if everybody did" what it is convenient or entertaining for them to do in isolation.
Some of the issues covered in the book might feel a little constraining for families with relaxed standards of physical behavior - it covers such issues as rough play, "changing your seat," and slamming doors - but the words are few and the illustrations are pretty hilarious if you ask Z and I, so it's easy to focus the "lesson" on the standards you actually care about enforcing. Consequences include doors falling off and crushing everyone, a sea of unseated children chaotically shifting positions around a room, and (for the action shown above) a pile of people laying like pancakes while the last of a dozen or so people gleefully leaps towards the dogpile.
Proof that this book is serving us well was close at hand recently. Jenni was sick with a cold and dropping used tissues on the floor (there was no trash can handy) and Z waltzed up and "corrected" her. "Mama, what would happen if EVERYBODY did that?"

Personally, this one cracks me up - Stover has an eye for details. The kid with his hands in his mouth makes me laugh every time.
You can pick up
If Everybody Did on Amazon.com for about eight bucks.
- Jeremiah