Start a verbal story for your child. You can make it anything, but the more ridiculous the better. Tell a story about a mouse that lived in the freezer section of the grocery store. Use a "mouse voice" to express the words of the mouse.
Ask your child to pick up at the mid-point of your story and tell more of it, or tell one of his own. You can help him with ideas that he can use for his story. Enjoy the exchange of ideas to show how stories are a great deal of fun to create.
Expand the ideas to be written down on paper. You may want to transcribe one of your child's stories at first to encourage her. When you teach creative writing, develop the concept of saving the story for reading aloud later.
Have your child write something short on a topic he likes. Just five to 10 lines will suffice, and explain that the writing can be purely imaginative or can contain something from real life. Help him by suggesting a general topic. For example, choose a summer afternoon as the topic and have him mix his imagination with facts. Using something factual as the basis, such as images of his grandparent's house or his pet cat, can help him expand with creative ideas.
Encourage your child to write a while story by herself. You can help her by providing a starter to the story. Give her some time and then ask her to read the story aloud to you. Explain that you aren't going to read over the story yourself, so she doesn't have to worry about spelling, grammar or punctuation. Never judge the creativity. Interesting tales can be developed if allowed to develop in a nurturing environment. Telling the story aloud gives your child an opportunity to be center stage and allows you to ask questions that will encourage more description.