Be sure to plug in Taxpayer Identification Numbers (usually Social Security Numbers) for your children and other dependents on your return. Otherwise, the IRS will deny the personal exemption of $3,700 for each dependent and the $1,000 child tax credit for each child under age 17.
Be especially careful if you are divorced. Only one of you can claim your children as dependents, and the IRS has been checking closely lately to make sure spouses aren’t both using their children as a deduction. If you forget to include a Social Security number for a child, or if you and your ex-spouse both claim the same child, it’s highly likely that the processing of your return (and any refund you’re expecting) will come to a screeching halt while the IRS contacts you to straighten things out.
The $1,000 child tax credit begins to phase out at $110,000 for married couples filing jointly and at $75,000 for heads of households.
After you have a baby, be sure to file for your child’s Social Security card right away so you have the number ready at tax time. Many hospitals will do this automatically for you. If you don’t have the number you need by the tax filing deadline, the IRS says you should file for an extension rather than sending in a return without a required Social Security number.