I generally do my expenses so that one child's money goes in the bank and is not touched at all for the year. This money is ear marked for things like taxes or to help out if something major happens and needs to be repaired or whatever. Which means when budgeting for household things I plan on the income from 3 kids and that is what we live within. That means I have money set aside for taxes, and when I am full I have one child's worth of non earmarked money that can be used for the frills and extras.