Asking you to do a literacy based starter to a class is weird - will you be delivering lessons as part of the role? And it's strange the suggest it should be literacy based, whereas I imagine your role is going to be more focused on encouraging kids to read for pleasure, than to develop their literacy. 15 minutes is also long for a starter activity.
I think on balance I would create a resource where you pick three or four current popular kids' books from different genres and give the students the blurbs on the back, and an image of the cover. And give them a photocopied table with a few key questions about each one (what do they predict it will be about, what genre do they think it is, do they anticipate enjoying it, etc). Then at the end ask them to pick the one they would choose and give a reason why. And do a Q and A for that bit where you pick four or five kids to give their answer. (Warn them you will be doing this beforehand - maybe reward students who answer with a lollipop or something).
This would demonstrate:
A knowledge of current kids' fiction (if you don't have this Google is you friend)
An ability to create attractive and user friendly resources.
An ability to ask questions of kids and praise and reward good answers. If possible ask a few open questions to get the ones who answer to develop their responses.
It might be worth asking if you are allowed any further info on the kids you will be working with, such as whether any of them have any SEND that would require adapted resources (such as needing them printed on coloured paper etc). This will demonstrate you take planning and SEND seriously.
In terms of the interview, school librarian roles vary from school to school, but schools tend to be looking for:
- someone who will engage in meaningful professional relationships with the kids, and show an awareness and responsiveness to different individual needs etc.
- someone with a passion for developing reading for pleasure, and ideas about how you can do this such as author visits, book clubs, competitions, etc.
- ideas about fund raising, filling in grant applications etc
- skill at display etc, and making the library an attractive space
- strong organisational and time management skills
- ideas on how you will work with the departments, especially English.
- passion for reading and some knowledge of current children's literature.
Good luck! It's an amazing job and such an important one!