Macbeth is a drama obsessed with children, in a peculiarly anguished, throttled manner. Launcelot Gobbo, in The Merchant of Venice, remarks that “it is a wise father that knows his own child” (2.2.76–77); and throughout Macbeth the characters in the play, and we in the audience, are frustrated in the attempt to make sense of paternal and filial relationships. In healthy families, kinship is clear—we know that Malcolm is the son of Duncan, and that Fleance is the son of Banquo. And in a healthy state, feudal obligations are clear, in that lord and vassal are defined, through metaphors of parent and child, as forms of love—as Macbeth tells Duncan:

But in unhealthy families, such as Macbeth's, children twist and recede, grow phantasmagorical. Macbeth understands his children as the consequences of his deeds; and as he becomes a bad child to Duncan, his own “children”—the results of his murderous acts—become monsters, turn against him. The stage starts to fill with various sorts of gruesome or dead children—emblems of the distortions and emptinesses that an evil present can inflict upon the future.

The assassination of Duncan feels, to the assassins, exactly like patricide. Lady Macbeth is so sensitive to Duncan's fatherlikeness that she can't stab him: “Had he not resembled / My father as he slept, I had done’t” (2.2.12–13). As soon as Macbeth commits the crime, he enters an odd sort of familial limbo, where no one has any sense of who is parent and who is child. By unchilding themselves from the family of Duncan, Macbeth and his wife become monsters, and start to engender further monsters. King James, in the Daemonologie, was skeptical about the existence of changelings, freaks born from the intercourse of an incubus and a witch—James thought that the devil could take “intollerably cold” sperm from a corpse, and deposit it in a mortal woman, but that “it would bread no monster, but onely such a naturall of-spring, as would haue cummed betuixt that man or woman and that other abused person, in-case they both being aliue had had a doe with other.”