Their murders are emblematic (symbolic) of Macbeth's excessive bloodthirst, they presented no threat yet he is now on an unstoppabletrajectory of murder.
They are symbols of innocence, the dialogue between Lady Macduff and her son is intimate.
It shows the natural maternal bond.
Lady Macduff speaks in the semantic field of birds, comparing herself to a "diminutive" "wren" which characterizes them as prey.
Thus, securing Macbeth within the role of the predator.
This is the first murder to occur on stage.
Suggesting that Macbeth no longer cares for his reputation and takes pride in his heinous acts.