The opening clip of 'Children of Men' contains a vary of shots and sounds, a successful opening sequence should contain. I think the first form of clear narrative is shown within the combination of the first shot and sound. Without the 'BCC' news report playing in the cafe, we would have no idea what the narrative of the film is, therefore the clarity of the narrative relies on sound in the opening clip. Although the non-verbal aspect (first shot) of the scene adds to the understanding of the narrative. The crowd watching the news in the cafe all wear facial expressions of shock and sheer sadness.
We then meet the main character