Albert Barnes on Matthew 21:15-16

When the Chief Priests. The chief men of the nation were envious of his popularity. They could not prevent it; but being determined to find fault, they took occasion to do so from the shouts of the children. Men often are offended that children have anything to do with religion, and deem it very improper that they should rejoice that the Saviour has come. Our Lord Jesus viewed this subject differently. He saw that it was proper that they should rejoice. They are interested in the concerns of religion; and then, before evil principles get fast hold of their minds, is a proper time to love and obey him. He confounded them by appealing to a text of their own Scriptures. This text is found in Ps 8:2. This quotation is not made directly from the Hebrew, but from the Greek translation. This, however, should create no difficulty. The point of the quotation was to prove that children might offer praise to God. This is expressed in both the Hebrew and the Greek.

(f) "Hosanna" Mt 21:9