Teach students to tell their tales in controlled scribbles rather than in words.
Let them scribble, from left to right, on a large surface, such as a lined chalkboard or on experience chart paper clipped to an easel.

They can use simple punctuation here and there with occasional capital letters if they wish.
When a story is complete, the child "reads" it to the class.

Don't be surprised when authors reread some of their scribbled sentences to correct "mistakes."

Extension:
On a regular basis, have children identify examples of fact and opinion in the print and nonprint materials they use, such as books, newspapers, magazines, films, TV, radio and so on.