How does the opening of 'City of God' set the tone, genre and themes of the film through the use of micro elements?

In the opening of 'City of God', the main theme that is represented evidently throughout is violence. This is shown through the micro elements of mise en scene and cinematography as the first scene shows Lil Ze and his gang. They specifically used close up shots as the audience would be able to see their facial features clear enough to identify the fact that these boys are too young to be exposed to a world of pain and cruelty. This suggests from the ages they are presumed by the shots of them, it would be expected for them to still be innocent and vulnerable however in the close up's we see them using guns and knives to chase around a chicken. Therefore this creates the idea that the environment being filmed isn't safe at all, from the cinematography it is shown to be run down which could suggest the reasoning behind boys at such an early age being open to violence. As well as before the chicken chase has even started, there are multiple shots of the other chickens being slaughtered as they are cross cut from the chickens to the drinks being made and the characters are shown to be having a good time. Furthermore, this has been purposely done to juxtapose the visual and sound as the atmosphere is shown to be fun and light hearted however this is contradicted by the fact that the chickens are being killed.