Deductions & credits

In the left-side menu, click on Tax Tools > Tools, then choose 'View Tax Summary' from the pop-up menu.

Back at the left-side menu, choose 'Preview my 1040'.

When your tax return opens, scroll down to Line 19 and see if $500 is entered as Child Tax Credit, then scroll down to Line 28 and see if $1500 is entered as Additional Child Tax Credit.  If you owed no tax (and it sounds like you don't) you should still receive the $1500 Additional Child Tax Credit. 

Here's more info about the Child Tax Credit.