Good Night, Maman — Norma Fox Mazer

Dearest Maman, In June 1940, twelve-year-old Karin Levi's world is torn apart as the German army occupies Paris. Karin, her older brother, Marc, and their maman must flee, seeking safety wherever they can find it. But Maman falls ill and is unable to travel, forcing Karin and Marc to leave her behind. When Marc manages to obtain two coveted places aboard a ship bound for America, the distance between them grows even greater. Will Karin ever see her beloved maman again?