Imagine you are directing Act IV, scene ii of Macbeth: design the set; dress Lady Macduff and her son; and direct the action.
To maximize the sense of innocence
- i.e. the more innocent Lady Macduff and her son seem to the audience, the more cruel their murders seem, and the more wicked Macbeth will look.
You will first need to consider the sense of innocence (I assume you are looking for contrast with the evil in other characters and moments in the play.) as an overall theme that appears in more than just one scene in the play. Anyone directing a production of Macbeth (or any other play), would begin with the larger picture of the play and then make sure the overall design and approach is carried out with each character and costume. So, though you ask about one scene, a director would never create elements for one scene without having first considered the play as a whole.
That said, if you do look just at this scene, the symbolism of innocence, commonly represented by white, is always an obvious choice. White costumes, bright white lighting, white drapes adorning the space. Do you want to be very heavy-handed? Have Lady Macduff and her son interrupted at prayer or while reading their Bible, since innocence and religious piety are often conjoined. And cleanliness. Innocence can be suggested by how very clean everything is. Maybe she is bathing her son?
The innocence of Lady Macduff and her son can also be highlighted by how they are contrasted by the murderers. They are dressed in dark, dirty clothes and act in very irreverent and crass ways. And, of course, the blood you could fling around, spewing on all that white, could highlight the innocence betrayed and defiled.
I hope these ideas help you to create your own staging of the scene.
Lady Macduff should be dressed in very fine clothing. She is a Lady, the wife of the Thane of Fyfe, and therefore a person of high standing. Her dress should be made of good quality cloth, with embroidery detail, perhaps even some lace. The colors should be relatively bright. Of course, she should be in the style of the the 12th century Scotland. Her son should also be dressed in fine clothing. His clothes should resemble an adult's so that he seems almost a miniature adult. Lady Macduff's demeanor should be one of wistfulness and sadness, mixed with a bit of fear, but with a firm determination underlying it all. When Ross enters, Lady Macduff"s determination becomes steely. She gets to vent her anger to Ross. When she talks to her son after Ross leaves, Lady Macduff's expression becomes one of love mixed with fear and sadness. She tells her son that his father is dead because she is angry that Macduff left his family to go to England to speak to Malcolm. She knows that she and her family are in danger because she knows that Macbeth considers them enemies. Her son is a bright child. He knows his mother is only toying with him, but he also knows that something is going on; that something isn't right. Thus he questions her. When the murderer enters the room, Lady Macduff tries to shield her child from the murderer as any good mother would. She resolutely stands up to the murderer defending her husband's name. The boy, loving his mother dearly, tells her to run even as he is being killed.