The custodial parent is the one allowed to claim the credit.
Child of divorced or separated parents or parents living apart.
Even if you can't claim your child as a
dependent, he or she is treated as your qualifying person if:
-
The child was under age 13 or wasn't physically or mentally able to care for himself or herself,
-
The child received over half of his
or her support during the calendar year from one or both parents who are
divorced or legally
separated under a decree of divorce
or separate maintenance, are separated under a written separation
agreement, or lived
apart at all times during the last 6
months of the calendar year,
-
The child was in the custody of one or both parents for more than half the year, and
-
You were the child's custodial parent.
The custodial parent is the parent with
whom the child lived for the greater number of nights in 2016. If the
child
was with each parent for an equal number of
nights, the custodial parent is the parent with the higher adjusted
gross income.
For details and an exception for a parent who
works at night, see Publication 501.
The noncustodial parent can't treat the
child as a qualifying person even if that parent is entitled to claim
the
child as a dependent under the special rules for
a child of divorced or separated parents.
https://www.irs.gov/publications/p503/ar02.html#en_US_2016_publink1000203279
