'Son's' in the Bible

So Zipporah took a flint, cut off her son’s foreskin, and threw it at Moses’ feet. Then she said, “You are a bridegroom of blood to me!”

And that thou mayest tell in the ears of thy son, and of thy son's son, what things I have wrought in Egypt, and my signs which I have done among them; that ye may know how that I am the LORD.