Little Children by Henry Morris, Ph.D.
 

"And Jesus called a little child unto him, and set him in the midst of them, And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven." (Matthew 18:2-3)

Many adult Christians have the mistaken notion that little children are too young to understand the gospel and so should not be allowed to decide for Christ until they are much older. The problem, however, is not the children; it is the adults who find it hard to understand! They must become like little children before they can really comprehend the way of salvation and be converted. Jesus said, "Suffer little children to come unto me, and forbid them not: for of such is the kingdom of God. . . . Whosoever shall not receive the kingdom of God as a little child shall in no wise enter therein" (Luke 18:16-17).

After all, what is there to understand? A very young child, instructed in the Scriptures from infancy as God has commanded his parents (note 2 Timothy 3:15, which uses the Greek word for "baby" as the state in which young Timothy began to know the Bible), can surely comprehend that the God to whom his parents pray made him, that he has sinned against God when he does wrong, that God sent His Son, Jesus, to die for his sins, and that Jesus can save him and take him to heaven. An adult may require much explanation and may imagine many difficulties, but a child will simply believe--and that's enough!

The word for "little child" or "little children" actually means children who are not much more than toddlers. It is the same word rendered "young child" when the wise men came to find Jesus in Bethlehem (Matthew 2:8, etc.). Little children should, by all means, be taught the gospel, and should be encouraged to come to Christ before they grow too old to understand with their hearts! HMM

http://www.icr.org/article/little-children/