After ‘War Horse’, this is another adaptation of a Great War tale from the pen of Michael Morpurgo, but this one holds the horses and focuses on two teen siblings caught in the conflict. When we meet Private Tommo Peaceful (George Mackay), he’s in a British army cell and looking doomed, before flashbacks pencil in a hardscrabble rural childhood and his defining bond with big brother Charlie (Jack O’Connell), also serving in the trenches. Bolshy, combative Charlie has always been there for the slighter, shy Tommo, but family and national loyalties are tested in the mud and blood of Flanders.Veteran director Pat O’Connor (‘Circle of Friends’) shows his old-school expertise in the charming country childhood sequences, where the film feels most individual and alive. When war arrives, the sense of outrage feels more generic, and the modest budget is desperately exposed in suggesting the scale of hostilities. There’s much over-egged mugging from the grown-ups (bumbling toff Richard Griffiths, shouty sarge John Lynch), but the lads are spot-on: young Mackay is effectively touching and bristling O’Connell hints at Next Big Thing charisma.