“They did not understand
What he said
καὶ αὐτοὶ οὐ συνῆκαν τὸ ῥῆμα ὃ ἐλάλησεν αὐτοῖς.
Luke indicates that Mary and Joseph did not understand what Jesus had said to them (καὶ αὐτοὶ οὐ συνῆκαν τὸ ῥῆμα ὃ ἐλάλησεν αὐτοῖς). They did not grasp or comprehend what he was talking about. Somehow, these parents of Jesus had no idea about who he was or what he was going to do. This seems odd, since his parents would have known him better than anyone else.