Charles Spurgeon addresses this...
"It is said by some that children cannot understand the great mysteries of religion. We even know some Sunday-school teachers who cautiously avoid mentioning the great doctrines of the gospel, because they think the children are not prepared to receive them. Alas! the same mistake has crept into the pulpit; for it is currently believed, among a certain class of preachers, that many of the doctrines of the Word of God, although true, are not fit to be taught to the people, since they would pervert them to their own destruction. Away with such priestcraft! Whatever God has revealed ought to be preached. Whatever HE has revealed, if I am not capable of understanding it, I will still believe and preach it. I do hold that there is no doctrine of the Word of God which a child, if he be capable of salvation, is not capable of receiving. I would have children taught all the great doctrines of truth without a solitary exception, that they may in their after days hold fast by them.
I can bear witness that children can understand the Scriptures; for I am sure that, when but a child, I could have discussed many a knotty point of controversial theology, having heard both sides of the question freely stated among my father's circle of friends. In fact, children are capable of understanding some things in early life, which we hardly understand afterwards. Children have eminently a simplicity of faith, and simplicity of faith is akin to the highest knowledge; indeed, I know not that there is much distinction between the simplicity of a child and the genius of the profoundest mind. He who receives things simply, as a child, will often have ideas which the man who is prone to make a syllogism of everything will never attain unto. If you wish to know whether children can be taught, I point you to many in our churches, and in pious families,—not prodigies, but such as we frequently see,—Timothys and Samuels, and little girls, too, who have early come to know a Saviour's love. As soon as a child is capable of being lost, it is capable of being saved. As soon as a child can sin, that child can, if God's grace assist it, believe and receive the Word of God. As soon as children can learn evil, be assured that they are competent, under the teaching of the Holy Spirit, to learn good."
"It is said by some that children cannot understand the great mysteries of religion. We even know some Sunday-school teachers who cautiously avoid mentioning the great doctrines of the gospel, because they think the children are not prepared to receive them. Alas! the same mistake has crept into the pulpit; for it is currently believed, among a certain class of preachers, that many of the doctrines of the Word of God, although true, are not fit to be taught to the people, since they would pervert them to their own destruction. Away with such priestcraft! Whatever God has revealed ought to be preached. Whatever HE has revealed, if I am not capable of understanding it, I will still believe and preach it. I do hold that there is no doctrine of the Word of God which a child, if he be capable of salvation, is not capable of receiving. I would have children taught all the great doctrines of truth without a solitary exception, that they may in their after days hold fast by them.
I can bear witness that children can understand the Scriptures; for I am sure that, when but a child, I could have discussed many a knotty point of controversial theology, having heard both sides of the question freely stated among my father's circle of friends. In fact, children are capable of understanding some things in early life, which we hardly understand afterwards. Children have eminently a simplicity of faith, and simplicity of faith is akin to the highest knowledge; indeed, I know not that there is much distinction between the simplicity of a child and the genius of the profoundest mind. He who receives things simply, as a child, will often have ideas which the man who is prone to make a syllogism of everything will never attain unto. If you wish to know whether children can be taught, I point you to many in our churches, and in pious families,—not prodigies, but such as we frequently see,—Timothys and Samuels, and little girls, too, who have early come to know a Saviour's love. As soon as a child is capable of being lost, it is capable of being saved. As soon as a child can sin, that child can, if God's grace assist it, believe and receive the Word of God. As soon as children can learn evil, be assured that they are competent, under the teaching of the Holy Spirit, to learn good."