The traditional understanding of the Church is that Mary took a vow of virginity that she planned to keep even within marriage. That is why her question to the angel, “How can this be, since I have no relations with man?” makes sense. Had she and Joseph been planning a normal marriage, she should have assumed that the angel was telling her that she would have a baby within the marriage in the way that women have babies once married.
Nevertheless, I would not go so far as to say that Mary’s vow of virginity meant that she “did not want children.” The Blessed Virgin had completely dedicated herself and her life to God. I would say that she wanted whatever God wanted for her, and if that plan for her included children, she was open to that.
