Black’s three laws of child-rearing

A friend asked me to post these rules that I've been spouting for years.

1. The work increases logarithmically with the number of children.
  Your first child is an infinite change in your life. From one to two is huge. From five to six? Nah.
  In case anyone cares, that's:   W(n) = W(1) + b log n , where W(n) is the work when you have n children, and b = [W(2) - W(1)] / log 2 .

2. The number of children you can take care of easily is always one fewer than the number of children you have now.
  When your second child is an infant, you marvel that the human race ever survived. When you have three kids and someone borrows one of them, you ask your spouse, "Is it quiet to you?"

3. It's not the number of kids; it's the number of kids in diapers.