William Hussey does a lot of work in schools, and by the sounds of things has some lively presentations based on the historical angle of witchfinders and so on. So if there's something historical in your books and you can work in costumes, props and roleplay I think you'll grab children's attention. It's worth checking out his site for inspiration: https://williamhussey.co.uk/contact/
My middle grade book is a fantasy starring a dragon and tiger, so I think dressing up is out the door unless I want to dress up like an animal. lol
When they reschedule, I plan on talking about how when I was their age I hated to read anything other than comics. It took finding the right book to catch my interest in 6th grade (Dragonlance Chronicles, for the record) to get me to start reading. Same with my daughter who helped me write the book. She hated to read until 4th grade when she found a book that caught her interest and now she reads more than I do. So, I was going to encourage them to try new things, read different things.
It sounds as if you have some good ideas for a presentation--now, if only you could present in a dragon costume!
Now you also have a great deal more time to plan.
When I was teaching, I taught almost entirely at the high school level, though I might have some techniques that could work with middle schoolers.
How long is your presentation supposed to be? Read a little and talk a little isn't very specific. If it's really a short time, it sounds as if you won't have much to worry about. The longer the time, the more creative you need to be. (Short attention spans--I blame TV.) Your idea of building a story with them sounds great, but that could require a somewhat longer time frame. Also, if the teacher is amenable, it would be a good idea to coordinate with him or her.
Students faced with an unfamiliar situation will sometimes freeze up. This even happens occasionally in high school. I've seen very vocal classes not know quite what to do with themselves when faced with a guest speaker. That's obviously a problem if you're doing anything that relies on audience-participation.
When I was presenting in high school, I had a home-court advantage because it was the school I used to teach at (at least a third of the students had relatives who were former students of mine). and I was helping them review for a mythology test based on a mythology book I wrote. Even so, the teachers prepped to avoid the possibility of dead air. One of them had the students write questions in advance. The other one worked out questions he could ask himself if the students needed to be kick-started. Both of those approaches worked.