Romans 5:14 "Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam's transgression, who is the figure of him that was to come."
Infants, dying in infancy, the Spirit of God tells us have not sinned “after the similitude of Adam’s transgression.” They, like all the human race, sinned in our father Adam. But God the Holy Ghost tells us plainly – “The soul that sinneth, it shall die. The son shall not bear the iniquity of the father” (Ezekiel 18:20). It is obvious then that dying infants, having committed no offence of their own, are chosen, redeemed, and born again by the grace of God, and must be saved.
These, is equally obvious, will constitute the great bulk of Christ’s kingdom at last. How else can he possibly have the pre-eminence in all things – in numbers, as well as in all other things? For it is only a little flock of the adult population of the world that belong to him in every age. But if you add to them the multiplied millions who die in infancy, you see him in possession of the multitude which no man can number, to shout his praises forever.