Child Benefit is payable to the parents or guardians of children under 16 years of age, or under 18 years of age if the child is in full-time education, Youthreach training or has a disability. I understand that child benefit is paid by the Department of Social Protection to only one beneficiary in respect of a qualifying child.
The person who receives the child benefit payment is being used as the initial indicator by the Revenue Commissioners to identify the individuals who are likely to qualify for the new credit. However, the credit will in the first place go to the person who cares for the child for most of the year. Agreement as to who will be the principal carer of a child is a matter for the parents or guardians.
It would be very difficult to administer the apportionment of the tax credit and extended standard rate band given the myriad potential child care arrangements possible. However, in cases like the one you have outlined, there is nothing to stop a primary carer claiming it in one year and relinquishing it to the non-primary carer for the following year.