“Look here!” The Greek word is idou (#2400 ἰδού), and it is used to get our attention. See commentary on Matthew 1:20 (“Look!).
“astonished.” This is a very powerful word; from the Greek ekplesso (#1605 ἐκπλήσσω). It designates an overwhelming astonishment: “to cause to be filled with amazement to the point of being overwhelmed” (BDAG). After days of diligently searching for their missing child, Joseph and Mary are flooded with emotions at his discovery.