This is actually a comment.

I have been having difficulties with this blog and it won't let me post comments. It also deleted my comment after I wrote it. Technology angers me. Anyway, if you're reading this, pretend it is a comment on Evan's post.

The witches never actually say that Banquo's children will be kings. They say only that Banquo will "get kings." (1.3.70) Macbeth and Banquo immediately assume this means Banquo's children would be kings, but there is another interpretation. Maybe, since Banquo's death was a major factor in the people of Scotland rebelling and Macbeth being overthrown, Banquo is considered as being the creator of the situation in which Malcolm took power. Banquo would then "get kings," (1.3.70), both getting Macbeth by removing him from the throne, and getting Malcolm, who he places on the throne. The witches may have only shown Macbeth the vision of kings looking like Banquo because Malcolm and his heirs will be a line of kings created by Banquo in a sense, even though they are not Banquo's descendants.