The actual marriage part of the wedding begins with the priest addressing the couple.
Priest: "Dearly beloved, you have come together into the house of the Church, so that in the presence of the Church’s minister and the community your intention to enter into Marriage may be strengthened by the Lord with a sacred seal. Christ abundantly blesses the love that binds you. Through a special Sacrament, he enriches and strengthens those he has already consecrated by Holy Baptism, that they may be faithful to each other for ever and assume all the responsibilities of married life. And so, in the presence of the Church, I ask you to state your intentions."
The priest then asks the couple a series of questions about their intentions.
1. First, he asks about the freedom of choice. In order for a marriage to take place, both parties must freely choose it. You are not free to marry, if you're married to someone else, or if you're being pressured or forced into marriage. Choosing marriage must be an act of free will. As I've said before, that is the way God operates; he never overrides free will.
Also, the priest asks about freedom of choice, because love is a choice in general. It is a conscious choice to desire the good of the other person. By choosing to love Katie and Katie alone, I am rejecting all the women who are not her.
2. Second, the priest asks the couple about their fidelity to each other. He says, "Are you prepared, as you follow the path of Marriage, to love and honor each other for as long as you both shall live?". Marriage is a life-long sacrament, and both parties must be fully committed to each other. Divorce is not possible, because the effects of marriage are permanent.
3. Third, the priest asks the couple if they are prepared to accept any children that God will give them, and raise the children as Catholics. This question is asked, because marriage is essentially life-giving. The couple must be open to life, rather than closed off by themselves.
The Catholic marriage rite mentions having children and raising children at several points, because that is one of the purposes of marriage. (The primary purpose of marriage is to grow in holiness.) Katie is partial to picking the options that mention children, because she has a daughter. There are options that do not mention having children, for the sake of older couples who are past child-bearing age.