Never Again, for Anyone by Stacy Friedman

From Arsenal Pulp Press: 

A gentle and loving children's picture book about a Jewish boy's compassion for others, including Palestinians

Lev loves learning about his Jewish culture and traditions. Ima, his mom, tells him about Bubbie, his great-grandmother, who had to pretend she wasn't Jewish when she was young in order to stay safe. Bubbie heard many people say, "Never again," but she always maintained, "We can't ever let anyone be treated like that again." Bubbie stood up for what she believed in.

When Lev sees a crowd including his friend Ameera marching for Palestine on the street outside his window, he asks Ima if they are speaking out for people being treated unfairly, just like Bubbie. Inspired by Lev's care and bravery, Ima takes him outside to join the march for Palestinian justice and the principle "never again, for anyone."