First remember that the gospels were written after the Lord has ascended. The writers would have had great difficulty severing the the level of understanding that they had themselves achieved from their stumbling confusion at the start of his adult ministery.
There is some evidence that Mary's sister Elizabeth had some understanding of what was taking place, but I see little evidence that Mary or Joseph understood more than that the child that they were raising was to be a King of the House of David. If you will remember, at one point the Lord came to despair at her lack of understanding during his adolescence, saying "what am I to do with thee woman?"
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“Some evidence?” I guess if one is determined to minimize the role of the Virgin, in fact make her virginity a mere sign, one must ignore the words of St. Elizabeth (Lk 1, 39-45) Mary (Lk, 46-55). Or do you think that Luke has put words into their mouths? Protestants are turned off by some of the excesses of Marian devotion. I have turned off by the disdain in which they hold the memory of the mother of our Lord.