One of the most relevant Bible questions for those parents who suffer through the terrible tragedy of losing a baby, or small child, is this: Will my precious child go to heaven? Therefore, the theological question is this: Does the Bible really teach the salvation of infants, or do we say such things just to make grieving parents feel better?
I personally believe that babies, though not old enough to be "saved" because they are incapable of understanding the gospel, are SAFE in the Lord's keeping until they reach the age of accountability. This is not just wishful thinking, or personal opinion--it is what Scripture consistently teaches us.
First, we have the fact that when God judged Israel for their unbelief in the wilderness, He spared all the children under 20 years of age. The entire adult population died during that 40 year period, but the children were spared from God's judgment. Read Numbers 14:29-32 to see this important truth. This is the first glimpse into the heart of God in regards to innocent children.
Second, when David was judged for his sin of adultery with Bathsheba, and his infant son died, he made this interesting declaration: "While the child was still alive, I fasted and wept: for I said, Who can tell whether God will be gracious to me, that the child might live? But now he is dead, why should I fast? Can I bring him back again? I shall go to him, but he shall not return to me" (II Sam. 12:22-23). Many parents, like King David, experience the grief that comes, even after fervent prayer, when a child still dies. But note here that David was confident he would one day see his son again in heaven.
Third, there is the account of Jonah's ministry to the city of Nineveh. He preached the destruction of their entire city, but God in His mercy decided to spare them from judgment. And here is the reason God gave Jonah for sparing the city from Divine wrath: "Should I not spare Nineveh, that great city, wherein are more than 120,000 persons that cannot discern between their right hand and their left hand?" In other words, God's reason for withholding His judgment on this wicked city was the tremendous number of innocent children that would die as "collateral damage".
Fourth, there is the very character of Christ, and His love for little children, as taught in both Matt. 18:1-10 and Matt. 19:13-14. In 18:6, Jesus pronounces judgment on anyone who would hurt a small child (modern day molesters) with these words: "But whoso shall offend one of these little ones which believe in Me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea!" Christ refers to childhood innocent faith by saying little children "believe in Me"--that is, they have not chosen to REJECT Him (like the Pharisees of His day). And then, in 19:14 we read: "Suffer (allow/permit) little children, and forbid them not, to come unto me, for of such is the kingdom of heaven". In other words, heaven will be filled with little children. Why? Simply because they are innocent, and do not have the mental capacity to either understand the gospel, or receive it.
On the basis of all these passages, we may safely conclude that children who die before the age of accountability are safe in the love of Christ, and will be in heaven where we will have the great joy of seeing them again!