The Hidden World — Graham Masterton

When Jessica's parents are tragically killed in a car crash, she goes to live with her grandparents in their big old house in Connecticut. Bullied at her new school because of the injury she suffered in the crash, Jessica finds solace in her favourite fairies and the pictures she loves to draw. One day she suffers bad concussion after falling downstairs at school, and while recovering at home she hears the strange sound of children's voices calling for help. At first Jessica cannot work out where the voices are coming from, but eventually she discovers from a mysterious but kindly old neighbour that they are in fact coming from inside her bedroom wallpaper. Attempting to overcome her own disbelief, Jessica and some friends venture into the world inside her wall where they find an extraordinary land where everyday household objects like spoons and hats take on a life of their own. But there is great danger to be found inside this hidden world, and it is up to Jessica to rescue the strange children whose voices she had heard, before it's too late.