(1) The annual rate of child support payable for a child for a day in a child support period is assessed under this Subdivision if:
(a) both parents of the child are to be assessed in respect of the costs of the child; and
(b) both parents are to be assessed only in respect of the costs of:
(i) that child; and
(ii) any other child in the child support case that relates to that child.
(2) Subsection (1) does not apply if at least one of the parents is liable to pay child support for a child under an administrative assessment under the law of a reciprocating jurisdiction.