A Child's innocence and the new birth:
I hear time and again claims that a child can "understand" the gospel. But is that what our Lord was saying in context when He said "except you have faith as a small child, you cannot see the Kingdom of God"? Absolutely not! The context of the passage shows this clearly:
Matthew 18:1 At the same time came the disciples unto Jesus, saying, Who is the greatest in the kingdom of heaven? 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. Whosoever therefore shall humble himself as this little child, the same is greatest in the kingdom of heaven.
Our Lord equates the new birth in adults to the safe innocence of a child.
To believe a child prior to puberty can be "born again" logically introduces the idea that children can also be condemned as a child. Condemned and sentenced to hell whether aborted in the womb or 11 years old. There cannot be one without the other, they are intertwined.
Our Lord used the illustration of child-like faith as the basis for true salvation in adults. He makes it clear that unadulterated, innocent faith is all that God notices.
Verily I say unto you, Whosoever shall not receive the kingdom of God as a little child, he shall not enter therein.
So the real question is when does a human being become accountable to God for their personal belief or unbelief?
in the above passages and the below, God's Word is consistent.
Eccles 12:1 Remember now thy Creator in the days of thy youth, while the evil days come not, nor the years draw nigh, when thou shalt say, I have no pleasure in them;
John 1: 6 There was a man sent from God, whose name was John. The same came for a witness, to bear witness of the Light, that all men through him might believe. He was not that Light, but was sent to bear witness of that Light. That was the true Light, which lighteth every man that cometh into the world. He was in the world, and the world was made by him, and the world knew him not.
Romans 1: Because that which may be known of God is manifest in them; for God hath shewed it unto them. For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:
A quick word Bible search for the word "blot" shows us clearly that all who are born are born with the knowledge of the Creator and with their NAME in the Book of Life of the Lamb slain from the foundation of the world. God declares this throughout the Old and the New Testaments. Here is one example of many and this occurs at the Great White Throne Judgment.
Revelation 3: 5 He that overcometh, the same shall be clothed in white raiment; and I will not blot out his name out of the book of life, but I will confess his name before my Father, and before his angels.
Here is an Old Testament example:
Exodus 32: 31 And Moses returned unto the LORD, and said, Oh, this people have sinned a great sin, and have made them gods of gold.
32 Yet now, if thou wilt forgive their sin--; and if not, blot me, I pray thee, out of thy book which thou hast written.
33 And the LORD said unto Moses, Whosoever hath sinned against me, him will I blot out of my book.
Once a child enters puberty, then the world begins to steal this UNDERSTANDING of the true Creator from their hearts.
Romans 1: Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
Professing themselves to be wise, they became fools,
All peoples are born with an open heart of innocence to God having this understanding God mentions in Romans Chapter 1. This understanding and innocent openness to God's Truth is built into them. Our righteous God holds NO ONE accountable until they are capable of forming their own opinion of God and truth.
For those who have raised children past puberty, it is not hard to understand. Once a child hits that age, their minds and hearts change as their hormones do. NOTE: The telling correlation between innocence lost as sexual maturity blooms. Mom and dad no longer know everything and the child begins to question, push back and formulate their own opinions on life, God and the world. This is when it is time for them to choose the broad and wide path to destruction, as almost all of them do. They do it because satan owns this world, and it social, cultural, and political systems. This is the time when their own national culture or their little piece of the world overwhelms them away from the True Creator to worship and serve the creature (whether their national religion is the darkest pagan or the prettiest catholic) or Godless humanism in all its pathetic forms. they begin to be capable of repentance toward God and saving faith towards our Lord Jesus Christ. Ask yourself: How can one repent when one has only borrowed opinions from parents and other influences as a child?
The Lord states that childlike faith is the standard by which saving faith for adults is judged. This is the purest form and without possessing that purest form of undoubted faith in the Lord, an accountable person cannot be saved.
Basic understanding that Jesus is God and loves them is evident in children when prompted by an adult but does that save?? I have never heard a single child ever say "OH NO HE ISN'T GOD" But knowing inherently by faith that Jesus is God as a little child is not repentance. Nor is it conversion. The point being, that conversion is not necessary or even possible for them at this point in life, they are not accountable.
Train them up in the way that they should go and when they are OLD, they will not depart from it. (sow the seeds, water them, when they are older, they will remember and will repent).
When a child expresses an opinion on God, politics or any subject other then liking candy that opinion came from an adult influence. All a child's cognoscente opinions are adopted from the parents or adult influences until puberty (or the Jewish age of accountability) which is another clue. Which also happened to be the age our Lord became Spiritually self-aware:
Luke 2:  Now his parents went to Jerusalem every year at the feast of the passover.
 And when he was twelve years old, they went up to Jerusalem after the custom of the feast.
 And when they had fulfilled the days, as they returned, the child Jesus tarried behind in Jerusalem; and Joseph and his mother knew not of it.
 But they, supposing him to have been in the company, went a day's journey; and they sought him among their kinsfolk and acquaintance.
 And when they found him not, they turned back again to Jerusalem, seeking him.
 And it came to pass, that after three days they found him in the temple, sitting in the midst of the doctors, both hearing them, and asking them questions.
 And all that heard him were astonished at his understanding and answers.
 And when they saw him, they were amazed: and his mother said unto him, Son, why hast thou thus dealt with us? behold, thy father and I have sought thee sorrowing.
 And he said unto them, How is it that ye sought me? wist ye not that I must be about my Father's business?
I have never met any child prior to puberty that understood repentance. Especially those talked into "inviting Jesus in the hearts" prior to puberty, they get it the least of all from my experience.
In addition there are plenty of examples of men and women believing on Christ in the New Testament. However, there is not one single example of a child repenting and expressing verbal belief on Christ in the New Testament and obviously children were around the Lord at times. Jesus says they inherently know Him, once again please read with a focus on verse 16:
Mark 10:13, And they brought young children to him, that he should touch them: and his disciples rebuked those that brought them.
14, But when Jesus saw it, he was much displeased, and said unto them, Suffer the little children to come unto me, and forbid them not: for of such is the kingdom of God.
15, Verily I say unto you, Whosoever shall not receive the kingdom of God as a little child, he shall not enter therein.
16, And he took them up in his arms, put his hands upon them, and blessed them.
That is it! no- go and sin no more; no- your sins be forgiven thee, no- thy faith have saved thee. You know, the things our Lord would tell every adult that came to Him and believed. Jesus simply hugged the children and blessed them. Heaven will be full of children. Will they rule and reign with Christ during His Millennial Kingdom? No, but they will be in Heaven. The multitudes in Heaven that our Lord references in Revelation are the children who have died in the womb or before the age of accountability. The minority in Heaven are and will be adult believers.
Revelation 7:9 After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;
If a person is of a sound mind after puberty, they are without excuse (Rom 1:20), anything before that or the mentally disabled are "with" excuse.
Nor are there any examples of the mentally incompetent receiving Christ either. These omissions are for a reason. The Bible is silent on the mentally incompetent apart from one passage that instructs us to "comfort the feeble minded". No Gospel, no preaching to repent but simply show kindness to them. Why? Common sense tells us why, they cannot repent because they are mentally unaccountable and safe before God.
Sure, God can do anything He wants and it would be right. BUT, does He teach that in His Word? Does He teach us His merciless cruelty to the mentally weak and helpless?
This brings up the question of those who have believed their whole life that they were "born again" as a child. These are people who were raised in churches and have remained in church since. Many pastors have this testimony, many Christian workers of all types have this testimony and untold numbers of various church members.
They started to take the narrow path by enlarge as children. Not many stick to it however. These are split into two types as all church members are: Wheat and tare. The majority of the those child baptisms become tares and will never know that they are. This is the fault of the apostate preachers they and their parents have been exposed to their whole life. The aim of most of their sermons as weeds is to reassure the weeds.
I have witnessed 100s of child baptisms all over the world having worked many years in the bus ministries of diverse IFB churches. From these experiences I have come to later realize that in every single church where child baptisms were commonplace they were done out of the service of mammon and not God. These are numbers, numbers are clout and reputation among these pastors. Reputation and clout brings notice by larger congregations. Notice by larger congregations could bring advanced career opportunities to these pastors. All under the guise of some "calling" if they impress these larger congregations. Calling to what? To higher salaries and more esteem among men.
But some actually do come under true conviction at a later point as adults, these get regenerated without knowing it at the point of true belief, having professed Christ so many years ago when they were safe. Although mistakenly referred to as "re-dedication", this event is typically their new birth from professing believer to possessing disciple.
John 3:8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit.