What is the "Right" Number of Children?

Clearly with four children, although only two successful pregnancies, I have my own idea on the "right"number of children, because I believe that all of mine were meant to be here.  However, popular thought is the following:

One - Population Control

Two - Parental Replacement

Three - Trying for a girl/boy, if first two are of the same sex.

Four or More - Too Many

What do you think is the number of children that families should have?  I'd love to know what you think.  Leave comments below.