Who gets to cliam the kids when its 50/50 custody, but the kids were with one parent the whole year around? Also, my ex didn't pay any child support for the entire year.

The court papers states that we each get to claim one, but the whole year around both my kids were with me. Also, he didn't pay any child support for them. Who gets to claim them? me who cared for them the whole year or my both of us?