Daddy Love by Joyce Carol Oates
The kidnapper, a part-time Preacher named Chester Cash, calls himself Daddy Love, as he has abducted, tortured, and raped several young boys into being his lover and as well as his 'son'. He confines Robbie in a device called an Wooden Maiden, in essence a small coffin, and renamed him 'Gideon'. Daddy Love slowly brainwashes 'Gideon' into believing that he is Daddy Love's real son, and any time the boy resists or rebels it is met with punishment beyond his wildest nightmares.
As Dinah recovers from her wounds, her world and her marriage struggle to exist every day. Though it seems hopeless, she keeps a flicker of hope alive that her son is still alive.
As Robbie grows older, he becomes more aware of just how monstrous Daddy Love truly is. Though as a small boy he as terrified of what might happen if he disobeyed Daddy Love, Robbie begins to realize that the longer he stays in the home of this demon, the greater chance he'll end up like Daddy Love's other 'sons' who were never heard from again. Somewhere within this tortured young boy lies a spark of rebellion...and soon he sees just what lengths he must go to in order to have any chance at survival.