Having a child renewed filmmaker Nanfu Wang's interest in China's one-child policy. In effect from 1979 to 2016, the restrictions on family size halted China's explosive population growth but have left the country with a rapidly aging population. From forced sterilizations and abortions to fines and propaganda campaigns, Wang examines how the policy was enforced in her new documentary, "One-Child Nation." The film won the grand jury prize at the Sundance Film Festival and recently screened at