"There were no baby-sitters then and Bumby would stay happy in his tall cage bed with his big, wonderful cat named F. Puss. There were people who said it was dangerous to leave a cat with a baby... F. Puss lay beside Bumby in the tall cage bed and watched the door with his big yellow eyes, and would let no one come near him when we were out... There was no need for baby-sitters. F. Puss was the baby-sitter."
-Ernest Hemingway, A Moveable Feast
[Disclaimer: No, I don't use my cat as a babysitter and I wouldn't recommend it. Unless of course you have a cat like F. Puss. :) ]