I do know Dunkirk is World War II - I mentioned World War I because that's where adaptations usually kill one of the boys off. In this case they made it through World War I (although not, in Dickon's case, unscarred) probably so the World War II London evacuee heroine could meet them all before Colin's Tragic Demise.

I also can't get over grumpy Dickon. I realize it real life that wars can have strange effects on people's characters and so forth and so on, but - Dickon! I could perhaps buy him as a mostly silent gardener that the heroine thinks is grumpy just because he's so quiet, but no, he's just plain grumpy.