Why is Mary a Virgin?
God willed that Jesus Christ should have a true human mother but only God himself as his Father, because he wanted to make a new beginning that could be credited to him alone and not to earthly forces.

Mary’s virginity is not some outdated mythological notion but rather fundamental to the life of Jesus. He was born of a woman but had no human father. Jesus Christ is a new beginning in the world that has been instituted from on high. In the Gospel of Luke, Mary asks the angel, “How can this be, since I have no husband?” (= do not sleep with a man, Lk 1:34); the angel answered, “The Holy Spirit will come upon you” (Lk 1:35). Although the Church from the earliest days was mocked on account of her belief in Mary’s virginity, she has always believed that her virginity is real and not merely symbolic.

Did Mary have other children besides Jesus?
No. Jesus is the only son of Mary in the physical sense.
Even in the early Church, Mary’s perpetual virginity was assumed, which rules out the possibility of Jesus having brothers and sisters from the same mother. In Aramaic, Jesus’ mother tongue, there is only one word for sibling and cousins. When the Gospels speak about the “brothers and sisters” of Jesus (for instance, in Mk 3:31-35), they are referring to Jesus’ close relatives.

Isn’t it improper to call Mary the “Mother” of God?
No. Anyone who calls Mary the Mother of God thereby professes that her Son is God.

As early Christianity was debating who Jesus was, the title Theotokos (“God-bearer”) became the hallmark for the orthodox interpretation of Sacred Scripture: Mary did not give birth merely to a man who then after his birth “became” God; rather, even in her womb her child is the true Son of God. This debate is not about Mary in the first place; rather, it is again the question of whether Jesus is true man and true God at the same time.