How does Protestant Church explain Luke 2:48?
The link below are numerous Protestant commentaries on Luke2:48
"And when they saw him, they were amazed: and his mother said to him, Son, why have you thus dealt with us? behold, your father and I have sought you sorrowing."
Verse-by-Verse Bible Commentary
To answer your other question;
Some denominations believe that Jesus had siblings on the earth. I am therefore, curious to know why Mary did not mention the said brothers and sisters who would have definitely joined the parents in the search for their dear brother Jesus, who was 12 years of age at that time . How does the Protestant Church explain the said omission ?
Some denominations believe that Jesus had siblings on the earth.
There are some denominations but this denominations interpretation contradicted the well-known Protestant Founders and Leaders in the 16th century who teaches that Mary had no other children other than Jesus;
The protestant reformers affirmed their belief that Mary, while remaining every-virgin, was truly the Mother of God. Here are only a few examples:
Martin Luther (1483-1546), On the Divine Motherhood of Mary, wrote:
In this work whereby she was made the Mother of God, so many and such great good things were given her that no one can grasp them. ... Not only was Mary the mother of him who is born [in Bethlehem], but of him who, before the world, was eternally born of the Father, from a Mother in time and at the same time man and God. (Weimer's The Works of Luther, English translation by Pelikan, Concordia, St. Louis, v. 7, p. 572.)
Luther wrote on the Virginity of Mary:
It is an article of faith that Mary is Mother of the Lord and still a virgin. ... Christ, we believe, came forth from a womb left perfectly intact. (Weimer's The Works of Luther, English translation by Pelikan, Concordia, St. Louis, v. 11, pp. 319-320; v. 6. p. 510.)
The French reformer John Calvin (1509-1564) also held that Mary was the Mother of God.
It cannot be denied that God in choosing and destining Mary to be the Mother of his Son, granted her the highest honor. ... Elizabeth called Mary Mother of the Lord, because the unity of the person in the two natures of Christ was such that she could have said that the mortal man engendered in the womb of Mary as at the same time the eternal God. (Calvini Opera, Corpus Reformatorum, Braunschweig-Berlin, 1863-1900, v. 45, p. 348, 35.)
Calvin also up held the perpetual virginity of Mary, as did the Swiss reformer, Ulrich Zwingli (1484-1531), who wrote:
I firmly believe that Mary, according to the words of the gospel as a pure Virgin brought forth for us the Son of God and in childbirth and after childbirth forever remained a pure, intact Virgin. (Zwingli Opera, Corpus Reformatorum, Berlin, 1905, v. 1, p. 424.)
Your next question is;
I am therefore, curious to know why Mary did not mention the said brothers and sisters who would have definitely joined the parents in the search for their dear brother Jesus, who was 12 years of age at that time . How does the Protestant Church explain the said omission ?
Mary did not mentioned other brothers & sisters because they do not exist and the well-known Protestant Reformers upheld the teaching that Jesus had no other siblings.
How does the Protestant Church explain the said omission ?
If we follow the Protestant Reformers like Martin Luther, Zwingli, Calvin, etc teaching it is very clear that there's no ommision. But the New Protestant Reformers are the one introducing the novelty which Jesus solidly refuted in John19:26-27 when He entrusted His beloved Mother Mary to His beloved apostle St.John, erasing the confusions that Jesus had other siblings.
“Woman, Behold Your Son…Behold Your Mother”(John19:26-27)