John Chrysostom

The Lord truly did no miracle in His childhood, yet this one fact St. Luke mentions, which made men look with wonder upon Him.

Catena Aurea by Aquinas ↗

Theophylact of Ohrid

And all "were amazed." Do you see how He was advancing in wisdom, so that for many He became an object of curiosity and wonder? For the manifestation of His wisdom is His very advancement.

Commentary on Luke ↗

Bede

And all who heard him were astonished at his wisdom and answers, and seeing him, they were amazed. Note the distinction of words, and diligently examine the mysteries of your salvation and faith. They were astonished at what they heard from him, and seeing him, they were amazed. And they were all the more astonished at the wisdom of his answers, the more they despised the fewness of his years seeing it. His tongue revealed divine wisdom, but his age pretended human infirmity. …

On the Gospel of Luke ↗

Bonaventure

And they were astonished, etc. Here after the humiliation he adds the clarification: when it is said: And all who heard him were astonished at his understanding and his answers: because he answered most wisely, beyond estimation. For astonishment arises from an unusual and great impression: below in chapter five: "Astonishment seized them all"; Job twelve: "He leads counselors to a foolish end and judges to astonishment." And thus was fulfilled that saying of Wisdom eight: "On account of her I shall have glory among the multitudes …

Commentary on Luke, Chapter 2 ↗