what is the purpose of introducing macduff's son into the play?
In Act 4 scene 2 of Macbeth Lady Macduff and her young son are brutally murdered. Of all the deaths in the play, this is one that is seen on stage in all of its brutality. Macbeth has sent the murders to kill the entire Macduff family because he realizes that Macduff knows he had something to do with Duncan's death.
When the murders enter, they ask Lady Macduff, "Where is your husband?" but since he is not there, they continue with their mission and kill Lady Macduff and her son.
SON: He has kill'd me, Mother.
Run away, I pray you!Exit [Lady Macduff], crying “Murder!”
This brutal death of the young, innocent Macduff shows us how far Macbeth has changed since the beginning of the play. When the play began, he had to be convinced to kill King Duncan, but he has since killed a friend, and now his wrath includes killing both women and children.