out of the mouths of babes

Young and inexperienced persons often can be remarkably wise, as in She’s only six but she said, quite rightly, that Harry was afraid of the sitter—out of the mouths of babes, Mother said. This expression is a shortening and revision of expressions in the Old and New Testaments of the Bible. In Psalms 8:2, God ordains strength out of the mouth of babes and sucklings; in Matthew 21:16, praise comes from this source. Later generations changed strength and praise to wisdom.