Psalms 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.
Matthew 21:16: And said unto him, Hearest thou what these say? And Jesus saith unto them, Yea; have ye never read, Out of the mouth of babes and sucklings thou hast perfected praise?
‘"Out of the mouths of babes," we now say (slightly misquoting), come the darndest things. Children sometimes speak, in their simplicity, more wisely than their elders.
But adults will notice that, in coining this phrase, the author of Psalm 8 (allegedly David) isn't talking about darling little remarks or amusing notes. What he is talking about depends on the translation. In the King James Version, the Lord "ordains strength" (issues strong words) against his enemies, even through "babes and sucklings." In the New English Bible, babes likewise "rebuke the mighty." But in the Revised Standard Version and in the Jerusalem Bible, the little ones chant the glory and majesty of the Lord.
Though translators can't agree on whether the Psalmist's babes spout fighting words or waft hosannas -- either way it's a miracle -- Jesus preferred the latter. When the chief priests and scribes of the Jerusalem Temple cringe at the din of children crying "Hosanna to the son of David," Jesus scolds them: "Yea, have ye never read, Out of the mouth of babes and sucklings thou hast perfected praise?" (Matthew 21: 16). Jesus' quote, or rather paraphrase, is the main reason "out of the mouths of babes" became a popular catchphrase. But it didn't ensure the phrase would be well employed. ‘
Michael Macrone,
http://www.gracecathedral.org/enrichment/brush_excerpts/brush_20050816.shtml