All Our Children, the first play by the experienced theater and opera director Stephen Unwin, is structured as a moral debate that sheds light on the mass murder of disabled children in Nazi Germany. The play is well-staged and intermittently powerful, but overly schematic, as the characters too often feel like mouthpieces rather than fully realized individuals. It premiered on the West End in London in 2017, and now comes to the Black Box Theater at the Sheen Center, with a new cast, under the sure-handed direction of Ethan McSweeny.