Here is a verse written by David which Jesus quoted.
“Out of the mouth of babes and nursing infants You have ordained strength,” (Psalm 8:2 NKJV).
Jesus had entered Jerusalem on Palm Sunday as we know it and was healing and teaching. The people were shouting “Hosanna to the Son of David” and the religious leaders were “sore displeased.”
Jesus told them, “Yes. Have you never read, ‘Out of the mouth of babes and nursing infants You have perfected praise'” (Matthew 21:16 NKJV)? Jesus quoted it and made it about praise.
Praise would come from those who just displayed simple faith in Jesus. That’s praise as a child who trusts.
In another place Jesus said, “Verily I say to you, whoever shall not receive the kingdom of God as a little child, he shall not enter therein” (Mark 10:15). The only way you can enter the kingdom is with the simple faith of a trusting child. Adults make it so complicated. Children don’t have the hang-ups and the unbelieving questions that fill the mind of the unbeliever.
Jesus said grace is simple. You receive by faith without trying to figure everything out. It is all about His favor on you.