Fly Away Home (2016) -it's based on an autobiographical book of an austrian writer, where she recalls the last days of WW2, when she was a child

Wunderkinder (2011) -incredibly heartbreaking german movie about three musically gifted children during WW2

When Hitler Stole Pink Rabbit (2019) -based on the semi-autobiographical novel of the same name (not as tragic as the others)

Wolfskinder (2013) -about a bunch of so-called wolf children (street children surviving on their own during and after WW2)

And I second "The White Ribbon"

(Actually "The Boy in the Striped Pyjama" is for great parts not very realistic... just wanted to let you know.)