[11] And entering into the house, they found the child with Mary his mother, and falling down they adored him; and opening their treasures, they offered him gifts; gold, frankincense, and myrrh. [12] And having received an answer in sleep that they should not return to Herod, they went back another way into their country. [13] And after they were departed, behold an angel of the Lord appeared in sleep to Joseph, saying: Arise, and take the child and his mother, and fly into Egypt: and be there until I shall tell thee. For it will come to pass that Herod will seek the child to destroy him. [14] Who arose, and took the child and his mother by night, and retired into Egypt: and he was there until the death of Herod: [15] That it might be fulfilled which the Lord spoke by the prophet, saying: Out of Egypt have I called my son.
I guess I should rephrase my question:
It's obvious that St. Joseph was still alive in verse 13, so WHY did Holy Scripture specifically mention "the child with Mary his mother" in verse 11?
Perhaps this was one of the problems/questions addressed by the commentary in question (which might have been Life of Christ by Fillion), but I've forgotten the answer.