A Thunderous Whisper  (English, Hardcover, Gonzalez Christina Diaz)

Ani believes she is just an insignificant whisper of a 12-year-old girl in a loud world. This is what her mother tells her anyway. Her father made her feel important, but he's been off fighting in Spain's Civil War, and his voice in her head is fading. Then she meets Mathias. His family has just moved to Guernica and he's as far from a whisper as a 14-year-old boy can be. Ani thinks Mathias is more like lightning. A boy of action. Mathias's father is part of a spy network and soon Ani finds herself helping him deliver messages to other members of the underground. She's actually making a difference in the world. 

And then her world explodes. The sleepy little market town of Guernica is destroyed by Nazi bombers. In one afternoon Ani loses her city, her home, her mother. But in helping the other survivors, Ani gains a sense of her own strength. And she and Mathias make plans to fight back in their own unique way.