Question of the day: What's the ideal No. of children couples should have?

Our parents and grand parents had as many as seven children, some even ten or more but things have kinda changed now. So in this day and age what's the ideal number of children couples should have, no matter how rich or poor they are - just the average?
A. 2
B. 3
C. 4
D. As many children as they can afford ?