Children of Swallow Fell by Julia Green (author)

The world’s in trouble.
When war comes to the heart of the Italian city where Isabella lives with her family, everything changes. She makes the long journey with her dad to a safer place – the old house where he grew up in the north of England.
Isabella must adapt to a completely different life. No shops, no electricity, no phone signal. No friends or neighbours – until she meets two ‘wild’ children. Rowan and Kelda live by themselves, hidden from the world, survivors of the sickness that swept through the valley. When Dad fails to return from a trip to find food, Isabella has to work out what to do and how to survive. Together, can the children build a new life, a life for the future?
What do we really need for a happy life?