The Hiding Place by Winifred Mantle.
The Hiding Place is just what an adventure story for children should be: full of suspense, delightfully humorous and, through the skill of the author, entirely credible. The narration moves beautifully: there are always surprises round the corner. And the characters of the children, while mercifully free of sentimentality, are as irritating, endearing and funny by turns as children are in real life.