(1) This section applies if:
(a) 2 individuals are members of the same couple; and
(b) either or both of the individuals have a child from another relationship (whether before or after the 2 individuals became members of that couple).
(2) While the 2 individuals are members of that couple, each child who is a qualifying child of one member of the couple is taken also to be a qualifying child of the other member of the couple.