It isn't necessary, I wouldn't think. On the other hand, why is it necessary for you that she have other children? You can't prove it either way from the bible alone.
Ya know, the perpetual virginity of the Theotokos has been documented since before the canonization of the bible. The very group who you trust to put the correctly inspired books in the bible also venerated Mary as a perpetual virgin AND believed in the consecrated Eucharist as the Body and Blood of Jesus Christ.
I could be wrong by a hundred years or so, but the very first time Christians started to disbelieve in the perpetual virginity of the Virgin Mary was in the last couple of hundred years or so.
1) Because Scripture gives her the title of "virgin" (Isaiah 7.14, Matthew 1.23, Luke 1.27), which makes no sense if she subsequently had sex. 2) Because the creed calls her "the Virgin Mary". 3) Because it pleased God to arrange things in this way.
Mary having sex with her HUSBAND relates in NO WAY to the divinity of Jesus Christ, the Son of God.
Sure it does. To say that after Almighty God passed forth from her womb, that a man would dare to desecrate her be having sexual relations with her, is to deny the divinty of Christ. It is a statement that there is nothing particualrly Holy about giving birth to God the Word that would give one any pause from daring to touch that which God has so hallowed.
Certainly, this is not the attitude of Scripture towards those things which God has super-sanctified by his physical presence, such as the Ark of the Covenant and the Holy of Holies, both of which are figures of Blessed Mary. When men dared to touch the Ark, they were killed. When anyone besides the High Priest entered into the Holy of Holies they were killed. When Ezekiel saw God pass through the East Gate of the new Temple, the Lord made abundantly clear His thoughts on whether any man should dare have something to do with this entranceway:
And the Lord said to me: This gate shall be shut, it shall not be opened, and no man shall pass through it: because the Lord the God of Israel hath entered in by it, and it shall be shut (Ezekiel 44.2)
God entered the world through the womb and birth canal of the Blessed Virgin Mary. Afterwards, in accordance with His word, this passageway was shut up forever, and Mary remained inviolate.
It is an abominable blasphemous sacrilege to suggest that God felt the man-made objects such as the Holy of Holies and the Ark of the Covenant were too super-sacntified to be touched by the hands of mere mortals or entered into, but that the Virgin Mary, she whom he made "full of grace" and "blessed among women" was not, and took on the task of ordinary motherhood after giving birth to Jesus Christ, her firstborn Son apparently being such a trifle that she needed a goodly lot of others to supplement him.