Well, when you separate out housing, cars, health insurance, vacations, and education that doesn't leave a lot to fall specifically under the category of "children." If you pay for daycare, that's only a few years. For our family, the big expenses of having kids have been moving from a 1BR apartment to a 4BR house and getting a minivan. College (effectively planning to cover in-state tuition for them) will be a big one when the time comes.