“It smashes the head open like a melon.” 11 year-old Kevin Barry is in his kitchen, holding a hatchet up for the camera. He turns to his makeshift armoury. Here, he demonstrates, is how you throw a saw at someone running away. Kevin Barry is the youngest child in the O’Donnell family, who live in Derry’s Creggan estate, estranged from official ‘city of culture’ pride. His older brother, Philly, is currently exiled in Belfast, on orders of the neighbourhood’s Republican paramilitary enforcers. For his apparently drug-fuelled anti-social behaviour, Philly was sentenced by a secret vigilante panel and blasted in the back…