We need firstly to understand that all souls belong to God and he does what he wants. As Ezekiel 18:4 )KJV) states, "Behold, all souls are mine; as the soul of the father, so also the soul of the son is mine: the soul that sinneth, it shall die."
Furthermore, each person is culpable for their own wilful sins.
Ezekiel 18:20 (KJV) plainly states, "The soul that sinneth, it shall die. The son shall not bear the iniquity of the father, neither shall the father bear the iniquity of the son: the righteousness of the righteous shall be upon him, and the wickedness of the wicked shall be upon him."
As I study the scriptures, I find that there are two types of sin. The first is inherited from Adam and the punishment of it is death. We all die as a result of Adam's transgression. Paul wrote in 1 Corinthians 15:22 )KJV), "For as in Adam all die, even so in Christ shall all be made alive."
The second type of sin is wilful rebellion. We all know what that is so I need not go into it here. This is the sin which we must repent of.
Since all humanity is infected with the sin virus and all die, the death of babies is the payment for that sin of Adam. Furthermore, infants can't know good from evil so they are able to enter God's heaven.
This is one thorny subject which I plan on tackling in my next book called You Think You're Going to Heaven? People need to realize that there is no neutrality. Either you are the child of Christ or of Satan. That's just the way it is.