The Lady of Colours(1985)

In Quebec 40s, orphans or abandoned children are placed in a gigantic psychiatric hospital where children were locked. Were they sick? No, they simply had no family. To escape this oppressive universe, they created a parallel world: the institution's basement where, in a maze of tunnels, they founded an independent company, with its rituals, spells. A young girl, Agnes, reigns over this underground world that adults seem to tolerate.