I am married with 2 kids. How many deductions should each of us have on our W4?

Both wife and husband make a combined $180k / year ($110-husband / $70k-wife).  We have always filed jointly.  Ever since we had our kids, we have always had to pay at the end of the year.  How should we be claiming deductions on our W-4?  How many should the husband deduct, and how many should the wife deduct?  I want to Zero out at the end of the year, not pay.