No matter what, if you combine incomes, you will be subjected to a higher tax rate. Certainly having children can reduce your tax footprint, but you will still owe taxes more taxes due to your combined income. If you want to balance out the taxes you paid, you will have to use the Two Earner Worksheet at the back of your W-4.
My recommendation is to use more tax deductions, put more money towards your 401k (the max if possible, which is currently at $15000 each if I remember correctly), use your flexible spending accounts more aggressively, and find more deductions to use. Use the Two Earner Worksheet and account for the up to $30k worth of money you can put in your 401k and you might find that your taxes will improve.
(unless of course you have a job that does not have a 401k set up, where it gets harder…).
