When we had our first child we added up the cost for my wife to go to work and we made 50 cents an hour. She was working about 25 hours a week at the time. I picked up 2 extra hours a week and she stayed home. Came out ahead that way.
Yes, we definitely started coming out ahead when I quit my teaching job—even though we had two more kids after that. I would guess a large portion of families are paying for the “privilege” of having two absent parents.