You are simply incorrect.
1) The child was Divine; but his divinity was eternally pre-existant before Mary was.
2)He was a person.
3)As a man, he had a mother. As God, he could have no mother because a mother would pre-suppose a beginning.
The Marian heresy here is in elevating Mary to the position of divinity since something can not be the mother of something else that does not share its nature in at least the part one is referencing. I.E., A German Shepherd Mix has to have one parent that is of German Shepherd origin. Since Jesus is not a MIX, but is 100% Man and 100% God, and since Mary has no divinity within her, she can not have contributed to the Divinity of Jesus. She contributed to His biological humanity, which is miraculuously unified through the power of the Holy Spirit with His divinity.
Jesus was/is God. But not because of Mary.
My argument is sound. You chose the Nestorian option, the one that makes Mary only the mother of a nature, not the mother of a person.
-A8
The Catholic/Orthodox never said He was God because of Mary! Your reasoning is off the target, imo.
God the Word was God before He was Incarnate, after He was Incarnate and after He was born. Mary carried the Incarnate God in her womb and gave birth to God the Incarnate Word Who was named Jesus. That makes her the God-bearer (Theotokos), the Mother of God.