The entries on form 1040 on the lines we've suggested you look at tell the whole story. You've already said the amount on line 11 was 0. If line 11 is 0, it simply means you didn't have enough taxable income to qualify for the credit because you owe no taxes. Since you had no tax for the child tax credit to offset, you can't get it. But you may have received additional child tax credit instead and that's on line 17a of form 1040.
