When our second child was on the way, my wife and I attended a pre-birth class aimed at couples who had already had at least one child. The instructor raised the issue of breaking the news to the older child.
It went like this: "Some parents," she said, "tell the older child, 'We love you so much we decided to bring another child into this family.' But think about that. Ladies, what if your husband came home one day and said, 'Honey, I love you so much I decided to bring home another wife.'"
One of the women spoke up immediately. "Does she cook???"
During the spelling period the teacher asked the class: "Will anyone volunteer to spell matrimony?"
Little Johnny, being sort of a precocious young boy, stood up and promptly spelled matrimony.
"Now define it," said the teacher.
Little Johnny replied, "Well, I don't exactly know what it means, but my Aunt Mary says she's had enough of it."