Are they going to have time for a re-write?
It's a very short amount of time, plus re-writes take preparation over several sessions - & surely many of them will have missed a great deal of school, so are they really all going to be able to write?
The best advice I ever had for interview lessons was to keep things as simple as possible. Simple, simple, simple - and engaging. You want them to learn something, to feel happy and confident sharing what the know/have learnt with you, and to give them lots of opportunities to show you where they're at/what their understanding is.
Definitely look at the year 1 objectives and pick a simple target. Then choose a great book - children's literature is so great because the language is often fabulous & engaging, scaffolded with brilliant pictures.
There are so many objectives and interesting language features. Rhymes are fun - & phonically interesting (will the children pick out how rhymes 'work' - with the first sound changing & the last sound remaining the same? It's tricky but enormously rewarding for young people).
Adjectives are always great for children this age. It's so crucial to build on their excitement and enrich language.
And grammar - those crucial full stops and capitals, especially for proper nouns.
You could read a story, then as a class 'correct' a (very, very short) letter from a character.
I would suggest really simplifying your expectations of what they can manage. They're very small and they don't know you. Think of different ways that they can engage & demonstrate what they know/their engagement, other than a big 'task' at the end.
Do you have time to visit a children's bookshop? The classic children's books are classic for a reason. I'd suggest looking through a selection and choosing one that really grabs you with its language/story.