Fleance

From Shakespeare Wiki

Fleance was the son of Banquo in Macbeth. He has a very little role in the play, despite the fact that he plays a huge part in ensuring that Banquo's line lives on to become kings.

When he and his father were attacked by the three murderers, he was fortunately able to escape into the night. Where exactly he fled to is not certain (though some sources outside of the play say it was Wales).