We Who Stayed Behind (2008)

10-year-old Adam is one of few kids left behind, after all the grown-ups have been overwhelmed by fear and hopelessness and left the city. Adam tries to make sense of it all along with his friend Ida, but soon she too is struck by the same symptom of disillusion: her blood turns gray. Determined to put a stop to this madness and bring Ida back to life, Adam leads the children in their struggle to make the city a place worth living in once again.