"Nanny McPhee and the Big Bang" is a family film that follows the story of Nanny McPhee, a magical governess who arrives to help a widowed farmer and his unruly children during World War II. The children are initially resistant to her unconventional methods, but they soon learn valuable lessons about responsibility and teamwork. As Nanny McPhee uses her unique powers to guide the children, they face challenges from their mischievous cousins and the threat of losing their home. The film emphasizes themes of family, love, and the importance of accepting help from others in difficult times.