They can apply this deduction:

Women with children under three years old. If both parents are of the same sex (two male adoptive parents, two female adoptive parents, one biological mother and one adoptive mother or two adoptive mothers) both will be entitled to apply the deduction. In the case of a marriage of two men, the deduction is prorated equally. In the case of two married women, the deduction is prorated, except if one of the mothers is the biological mother. In the latter case, the deduction will only be applied to the biological mother.

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