I recall from my childhood reading a book where at the end the family partly change into birds. I remember a picture of the family in a nest and their arms have changed into wings. I read it myself so I think it is for around 7-8 year olds.
I recently bought a copy of the Twits by Roald Dahl and thought that it was this book that had that ending. But it isn't - the Twits get the shrinks!
So - please tell me which book I am thinking of, it is driving me crazy now.