Certainly not a whole version of the story in 3 sessions as free writing. New character would necessitate a new story. Maybe session one is learning the story, reception can do this as well. Session two you give children a copy of the story with gaps they can fill in with changes or simply retell the story as they wish. Reception ought to be able to do the retelling with support for spelling. (Differentiate this task as you see fit for your class.) Maybe use A5 paper and have just a sentence or two on each page at the bottom. Session three they illustrate and make their version into a book.