Hidden Yellow Stars by Rebecca Connolly

Based on the true story of two World War II heroines who risked everything to save Jewish children from the Gestapo by hiding them throughout Belgium.
Belgium, 1942.
Young schoolteacher Andrée Geulen secretly defies the Nazis in Belgium, who are forcing Jews to wear a yellow Star of David. Andrée is not Jewish, but she feels a maternal connection to her students, who are living in constant fear, and decides to take action. No child should have to suffer under such persecution. But what can one woman do against an entire army?
Ida Sterno is a Jewish woman who works with the Committee for the Defense of Jews in Belgium, a clandestine resistance group tasked with hiding children from the Gestapo. She wants to recruit Andrée because her Aryan appearance can provide crucial security measures for their efforts. Andrée agrees to join and begins work immediately by adopting a code name: Claude Fournier.
Together, Andrée and Ida, and their undercover operatives, work around the clock to move Jewish children from their families and smuggle them to safety through the secret channels established by the resistance. As each child is hidden, Andrée commits to memory their true name and history. Someday, she vows, she will help reunite as many of these families as she can.
But with the Gestapo closing in and the traitorous Fat Jacques who has turned from ally to enemy and is threatening to identify and expose any Jew he meets, Andrée and Ida must work even harder against increasingly impossible odds to save as many children as possible and keep them safely hidden-even if it might cost them their own lives.