Contradiction with Psalm 8:2
Matthew 21:16 cites this verse as fulfilled, but Psalm 8:2 attributes strength to infants through God's ordainment, not specifically as praise.
Psalm 8:2: Out of the mouth of babes and sucklings hast thou ordained strength because of thine enemies, that thou mightest still the enemy and the avenger. [ordained: Heb. founded]
Contradiction with Isaiah 29:13
While Matthew 21:16 emphasizes praise from the lips, Isaiah 29:13 speaks about people drawing near to God with their words but lacking sincerity in their hearts.
Isaiah 29:13: Wherefore the Lord said, Forasmuch as this people draw near [me] with their mouth, and with their lips do honour me, but have removed their heart far from me, and their fear toward me is taught by the precept of men:
Contradiction with 1 Corinthians 14:20
Matthew 21:16 highlights the virtue of childlike praise, whereas 1 Corinthians 14:20 advises believers to be mature in understanding, not acting as children.
1 Corinthians 14:20: Brethren, be not children in understanding: howbeit in malice be ye children, but in understanding be men. [men: Gr. perfect, or, of a ripe age]
Contradiction with Zechariah 9:9
Matthew 21:16 correlates praise with Jesus’ messianic entry, which Zechariah 9:9 predicts, but there is no mention of a specific praise from children in this prophecy.
Zechariah 9:9: Rejoice greatly, O daughter of Zion; shout, O daughter of Jerusalem: behold, thy King cometh unto thee: he [is] just, and having salvation; lowly, and riding upon an ass, and upon a colt the foal of an ass. [having...: or, saving himself]