Brundibar

From the legendary imagination of Maurice Sendak—creator of beloved classic Where the Wild Things Are—comes a classic tale of children cleverly overcoming a bully, retold by the Pulitzer Prize-winning playwright Tony Kushner.
Brundibar is based on a 1938 Czech opera for children that was performed fifty-five times by the children of Terezin, the Nazi concentration camp. When Aninku and Pepicek discover one morning that their mother is sick, they rush to town for milk to make her better. Their attempt to earn money by singing is thwarted by a bullying, bellowing hurdy-gurdy grinder, Brundibar, who tyrannizes the town square and chases all other street musicians away. Befriended by three intelligent talking animals and three hundred helpful schoolkids, brother and sister sing for the money to buy the milk, defeat the bully, and triumphantly return home. 
"An ambitious picture book that succeeds both as a simple children's story and as a compelling statement against tyranny." —School Library Journal