“One Child Nation” investigates China’s policy of pressuring families to have only one child. Filmmakers Nanfu Wang and Jialing Zhang grew up in China during the years of the policy that lasted from 1979 to 2015. Pure Nonfiction host Thom Powers interviews them about the making of the film and their strategies to avoid government surveillance and intimidation. Nanfu previously came under suspicion from Chinese authorities for her first film “Hooligan Sparrow” about a female human rights activist.