Director Kevin Macdonald had originally intended the cast to be all unknown or amateur actors and actresses and was looking for an American girl, around sixteen years old, to play Daisy, but cast Irish 18-year-old Saoirse Ronan instead, after her audition, reading a scene which left them in tears.
Director Kevin Macdonald chose to film the first half of this movie with a handheld camera to give the paradise-like countryside home a sense of humanity, as though the camera was alive and breathing. The second half of this movie was shot in a more steady and smoother style to make the war-torn countryside more sharp and unforgiving, as though the camera was mechanical.
In the book, Eddie and Isaac are twins, both fourteen years old, and they have an older brother called Osbert, who is sixteen. He hangs out with his friends and is not a part of the tight group of siblings with whom Daisy becomes close. In this movie, Eddie is older than Isaac and is the oldest sibling. Also, in this movie, Eddie communicates with animals - which is Isaac's trait in the book. In the book, Eddie can read people like Isaac can read animals.