Start simple. Choose a fairy tale, fable or parable with a moral and read it aloud to your class. Through the ages, Aesop, the brothers Grimm, Hans Christian Anderson, Andrew Lang, J.R.R. Tolkien and others have helped children and adults alike understand life lessons to avoid having to learn them the hard way.
Ask your students to identify the moral of the story. Examples: "King Midas" and "Rumpelstiltskin" taught not to be greedy. "Sleeping Beauty" and the "Emperor's New Clothes" taught about the disadvantages of vanity. "Little Red Riding Hood" taught not to trust strangers. More recently, "Charlotte's Web" was a story of persuasion itself---how a little spider could save the life of her best friend, Wilbur, with the power of the "pen," but with her miraculous web writing.
Have them think about an important lesson they have learned in their life, then write it down as a moral. For instance: Don't pull your dog's tail or stick your fingers in his mouth. Don't lie to your parents. What you do comes back to you.
Ask them to take that lesson and write a fairy tale with a beginning, middle and end, using their moral to persuade the rest of the class not to do what the character in their fairy tale did. Make sure they establish time and place. Does it take place in present day, the Middle Ages, prehistoric times, the distant future? Where is it set? In New York City? Belgium? A faraway island? A distant planet? Who is the protagonist, the hero? Someone their own age and gender? An elderly gent? A tree, bug, flying snake/dragon? What about the antagonist, the villain? A sweet little gray-haired lady? A dastardly used-car salesman with a pencil-thin mustache? Someone they thought was a friend? Let their imaginations run free.
Make sure to give them an opportunity to share their stories.