By claiming it on the tax return.

You didn't say what software you use, so I can't give any useful information about how to enter it in your software.

Sorry about that I am using proseries. 

On the W-2 worksheet, scroll down about 90% of the way to line K-c.  I think you are supposed to enter the amount there.

Then go to the "Find Form" and type "earn".  Open the Earned Inc Wks.   On the very top of that sheet, there are two checkboxes that you can include the include in earned income for purposes of the Earned Income Credit and the Additional Child Tax Credit.