Whomever has the child for 183 nights or more in the year is the custodial parent and can claim the child as a dependent on their tax return and the child tax credit on their tax return.
If the same child is claimed as a dependent on two separate tax returns, the IRS will start an investigation within a year after receiving the returns. The loser of the investigation will have to pay back any refund associated with the child as a dependent plus penalties and interest.
