For fans of P.D. James's novel The Children of Men, it is immediately clear that the movie has some drastic differences from the book. The film preserves the general universe, with apocalyptic infertility tearing humanity apart, and some of the characters, like Theo and Julian, but beyond that it creates a new storyline unique to the movie. This makes Alfonso Cuarón's directorial choices particularly evident: from the beginning, he had a clear vision for the film he hoped to create and was able to see it through to the end, crafting a piece that simultaneously entertains viewers and leaves them asking important questions long after the screen has gone dark.
Cuarón has said that one of his main objectives was to create a world that was futuristic, but not too futuristic—it had to be recognizable for viewers, and not distract from the main message with futuristic inventions like flying cars or supersonic gadgets. For this reason, he chose to shorten the timeline from thirty years since infertility began in the book, to just twenty-one years in the film. This meant that the world depicted in the film would be similar enough for audiences to recognize and connect with, making the subtle changes all the more jarring. Cuarón also kept the futuristic advances at a minimum in order to better connect the issue of immigrants and refugee treatment in the film with modern and historical crises like it, such as those in Iraq, Somalia, and Northern Ireland.
A technique characteristic of many of Cuarón's films is the "long take," which is one extended, uninterrupted shot of a particular scene, rather than a pieced together amalgamation of different camera shots to make a single scene. This is a challenge for filmmakers and actors, since everything must be done in one take, but it produces a raw, real feeling unmarred by camera close-ups or different angles used for effect. Children of Men features the long take in many of its scenes, notably in Kee's birth sequence as well as in many of the fight scenes that take place inside Bexhill.
Cuarón also noted that he did not want the film to be heavy-handed with the messages it projects; instead, he hoped that it would plant ideas and observations in the audience's mind so that they could come out with their own conclusions. For this reason, he leaves the film's conclusion very open-ended—there is a suggestion of hope for the future in the approaching Tomorrow ship and the sound of children's laughter, though nothing is confirmed, allowing audiences to construe their own assumptions.