The house where Michel meets the old lady who took care of his son is the house where Bertrand Tavernier lived his childhood with his parents during WWII. René Tavernier was a friend of Louis Aragon and Elsa Triolet.
The little girl on the train at the beginning of the film is Tiffany Tavernier, the filmmaker's daughter.
Bertrand Tavernier decided to use his home town of Lyon, which is rarely seen in movies despite its size, central location and economic influence. The movie doesn't show a postcard version of Lyon, as the Bellecour square or the Fourvière basilica are entirely absent from the movie, which is quite a feat. Instead, it mostly focuses on the Vieux Lyon (Old Lyon) neighborhood, which was quite a dismal state at the time, to the point where the mayor at the time planned to raze part of it. It is generally accepted that the success of the movie helped shine a light on the Vieux Lyon, which contributed to it being recognized as part of a UNESCO World Heritage Site in 1998.
The St-Paul prison where Michel visits his son at the end has been greatly transformed recently into university buildings.