With three rectangular boxes, start with the MIDDLE. This is where the action takes place. Keep it brief (may need support and practice to be able to write succinctly) eg 'dog lost in caves'.
Then fill in the first box outlining the beginning of the story/report using the 'W' word prompts: where, when, who, why, what can encourage relevant ideas. Finally fill in the end box. Then speak the story following the notes. Then write it.
Mind mapping can take many forms. A 'spider diagram' with a central topic with lines out to sub-headings leading onto further branches relating to them. A sheet of paper with words jotted down in random then circled and numbered once the brainstorming period has ended. Key words provided by the teacher which the pupil surrounds with associated ideas/words.
Another way is to start by drawing a picture. If a child has an idea for story or is required to express an event in their own words, they can draw one or more illustrations first to support the prompting and collation of ideas without being impinged upon by the written word.