You may not have enough tax liability to offset the full $2000 child tax credit. If so, you may be eligible for a part of the child tax credit and then another credit called the additional child tax credit that will make up the difference. If you Preview your tax return, you can see the child tax credit on line 12a of form 1040 and the additional child tax credit on line 17b.
To preview your return, click on Tax Tools then Tools then View Tax Summary. Look back to the left column and click on Preview My 1040.