The format of your lesson seems fine, but personally I wouldn't choose a traditional tale at this stage in the year. 'Traditional Tales' is a topic that basically all FS children cover earlier in the year, and I think you might find that they might be a bit "meh" about an overly-familiar topic. Personally I'd choose something different. Perhaps a Julia Donaldson book? She writes lovely simple stories that children engage well with. As for the writing, yes, certainly by this point in the year I'd be expecting all FS children to be having a good go at writing. Personally I'd model it with them first and then get them to have a go at writing "what happens next". Or perhaps get really creative and get them thinking about what happens to the character after the story ends, or a different ending completely! Doing that is a great generator of language and the children love coming up with some crazy ideas and might then be keener to have a go at the writing. Some should certainly be writing sentences, some only single words, but all should be able to have a go.