Nicolas Bary's first directorial effort, the 10000 euro, 10 minute-long short film Before... (2003) was already inspired by Henry Winterfeld's novel, and even already featured Armelle in the role of Corbac, the school teacher.
Nicolas Bary and producer/friend Dimitri Rassam (who's already produced Bary's third short Judas (2006)) spent no less than four years working on this film, from acquiring the film rights from Henry Winterfeld's heirs to the actual filming.
Nicolas Bary had already written a first draft of the screenplay when he met producer Dimitri Rassam, however it was deemed unsatisfactory, even by Bary himself. Nicolas Peufaillit was then hired and endeavored to distance himself from the book and modernize its characters, as he doesn't believe in straight literary adaptations. Thus, Bary and Peufaillit spent 18 months working together on the script, seeing each other every two or three days, acting out the scenes between themselves, creating new characters such as Mireille and Oscar's two bodyguards, injecting emotion and humor, and developing the bad guys.
Since the film is set at an indeterminate time, costume designer Patrick Lebreton mixed modern elements with accessories from the 1910s and the 1930s. He also closely followed the kids' casting process so as to match the costumes to their personality.
Nicolas Bary originally wanted to cast children with no prior acting experience, so as to get the most natural reactions on camera, but quickly backtracked when he realized that with so many kids in the cast, he should be able to rely on them if any problems were to arise.
Location scouting started in the Alsace region to the east of France, but the villages there were deemed too renovated. Scouting was then to continue in the Aveyron department, to the south, when Nicolas Bary learned that the film would likely be co-produced with Luxembourg and Belgium and decided to shoot the film in those two countries.
Nicolas Bary had just about given up hope on finding a satisfactory village and resigned to building one in studio when producer Dimitri Rassam heard by chance of a Wallonian (South Belgium) 17th century village that proved to be perfect.