In the Hail Mary, we say, “Blessed is the fruit of your womb. ” Jesus was holy from the very beginning. How can he be blessed by anyone?
That part of the prayer quotes Elizabeth’s greeting to Mary (Lk 1:42b). Elizabeth is not giving a blessing but simply acknowledging a blessing already given by God. If you sneeze and I say, “God bless you, ” I am not the source of that blessing but am simply recognizing that you have already been blessed by God.