So with you making 55k, and your spouse making 20k, and we'll assume at least 3600 in pre tax deductions (do you have pre tax retirement, fsa, hsa, health insurance?) your tax liability after the child tax credits pay the bulk of it, is 1100 or so. So check what your spouse has had withheld to date, and subtract that from 1100, and that's about what you can expect to owe.

Do you have the children in any paid daycare while you both work? That's another credit that could wipe away even that 1100.