A Rag, a Bone and a Hank of Hair by Nicholas Fisk
A gripping science-fiction novel set at the end of the 22nd century. The birthrate is falling following a nuclear power plant leak, and the government have begun manufacturing 'Reborns', new people from old. Brinm an arrogant twelve-year-old, is sent to live with a Reborn family, who have been recreated from 1940, to monitor the experiment. Initially he fears and dislikes them, but gradually becomes friends and tries to save them when the government decide to terminate the experiment.