Nobody Knows (2005)

Preteen Akira Fukushima (Yûya Yagira) and his young siblings have been abandoned by their mother, Keiko (You). Keiko, who has moved in with a new lover, has left Akira in charge of his brother, two sisters and a whole apartment, with little money and food to see them through. Akira and the other children, who were never enrolled in school, struggle to survive without basic amenities as they cope with a strange, solitary existence in a Tokyo apartment building.