In the context of defending marriage, people often talk about the common desire or the right of children to be raised by "a mother and a father." On reflection, the term "a mother and a father" makes the statement untrue, and misrepresents what marriage reality is: the sole institution that unites children with their own mother and father. It is important to try to break the habit of using this phrasing, which is in common usage and undermines communication about marriage reality.
Embedded in the phrase is the lie that mothers and fathers need not be specific to the child and are therefore interchangeable. If they are interchangeable, then that leads to a discussion of differences between men and women and if the sex of the parent really matters in terms of the good of the child. None of this is related to the reality of marriage.
The phrase "a man and a woman" in the context of marriage ignores the reality that every person without exception has a specific irreplaceable mother and father, and when someone loses one or both, even if they are adopted by a married man and woman, they are still in a state of privation of their own mother and father.
The statement is true when one says "There is a common desire and a right of children to be raised by their own mother and father."
We all have a common1 desire to know, be connected with, and loved by our own mother and father, even if we never knew them. That is an experience of God's plan for creation. And, we can confirm by our own experience, every child has a right to be raised in a family with his own mother and father united in marriage, because as the Church teaches, "it is through the secure and recognized relationship to his own parents that the child can discover his own identity and achieve his own proper human development."1
1 Common meaning to all and therefore to each.
2 Donum Vitae A1. Congregation for the Doctrine of the Faith. 1987