Does anyone know where I can find stories, which mix fantasy with WW2? Many thanks

There must be a lot that use evacuation as a way of moving characters to a place where magic can happen (Narnia, as you've already mentioned). Can't think of any right now! There's Carrie's War, but that's not really fantasy.

I think immediately of Bedknobs and Broomsticks! Wasn't that based on a book or books?

Bedknobs and Broomsticks is a lovely book - much more in it than the Disney: they time travel to all sorts of places.

Emma

Johnny and the bomb?

One - can't remember which, think it might have been "The Woven Path" - Wyrd Museum book, by Robin Jarvis, is in this genre. It's a YA fantasy novel.

Johnny and the Dead (Think it's Terry Pratchett.) Made into a picturesque tv kids series too.

The Book of Lost Things by John Connolly is about a boy who finds a way into a world full of characters from fairytales. I think it's set during WW2.

The ultimate one has to be Slaughterhouse 5 by Kurt Vonnegut..

check out the children's writers' group - there's a great one there (Cassandra)