Watch One Child Online at Couchtuner. “One Child”, a BBC Drama production for BBC Two, stars Harry Potter franchise alumna Katie Leung as Mei, a first-born Chinese girl adopted by English parents, who gets called back to Guangzhou when her birth mother desperately seeks her assistance in saving her son. How far will Mei go to help the woman who gave her away and the brother she’s never met? “One Child is a deeply affecting work that delves into the heart of a human struggle,” said SundanceTV President Sarah Barnett. “It tells the story of an ordinary young woman who is plunged into a situation that challenges her to her core.”