Even before the witches appear Justin Kurzel's 2015 adaptation of Macbeth actually starts with Lord and Lady Macbeth and their household at the funeral of a child. From the looks on their faces and seeing how they place things on the child's eyes and incinerate the pyre, it seems to be their child.
This child is picked up later in the film during Lady Macbeth's conscience-induced breakdown. When she holds her monologue about desperately cleaning her hands and not being able to deal with her guilt, it turns out she actually speaks (or imagines to speak) to her dead child.
As to my knowledge this child does not seem to be an aspect from the original play or other adaptations I have seen. So my question first of all would be if there is any precedent for Macbeth having a child that died, be it in any other adaptation, or maybe in the actual history of the real Macbeth, or even faint allusions in the original play that I'm just unaware of. Or is this really a brand new invention of this adapation?
Based on that, primarily if it turns out to be an addition solely done in this adaptation, I'd like to know in which way it adds to the characterization of Lord and Lady Macbeth. In which way does it paint their deeds and attitudes towards those deeds in a possibly new light, if it does? Or is there any information from the filmmakers why they chose to add it and what they thought it would contribute to the story and its themes?