Refreshing this thread because I was looking for a thread I started donkey's years ago, seeking help finding a book. Couldn't find that one, but refreshing is encouraged over starting anew, so here goes:

*British children's book in the E. Nesbitt or Enid Blyton family of types of children's books
*Set in the London Blitz years, I believe
*Children sent into the country to get them away from the War, I believe (like the Lion, the Witch and the Wardrobe)
*But these kids get sent to live with terrible people, in their minds, so they run/swim away to an island where they live out the War, I think, or whatever was keeping them away from their family in the city
*They build themselves a treehouse kind of shelter and swim some livestock over, chickens and maybe a mammal, sheep or cow?
*They spend one chapter dodging "day trippers" which as an American child I had no idea what they were but they were grownups who'd rowed over to spend the day on the island...

Anybody? Help? I lost the book on the Orient Express in the early '70's and have not been able to recall the title or the author, but it apparently isn't either Nesbitt or Blyton as I've gone through their bibliographies...