By way of background, we have to remember that everyone is guilty before God because of the sin we inherited from Adam (Rom. 5:12, cf. 1 Cor. 15:21-22). In fact, there is not a single righteous person (Rom. 3:10-11). We have all sinned (Rom. 3:23). Therefore, everyone is guilty before the holy, righteous God no matter how young or how old. Furthermore, belief is a necessary requirement for salvation (John 3:18-19, Acts 16:31).
While the Bible does not explicitly say where young children go when they die in infancy, it seems to imply that they go to Heaven.
First, there is no verse in Scripture which states that those unbelievers will go to Hell because they were not old enough to believe. Since God is just, it would appear that He would allow these infants to go to Heaven.
Second, perhaps the only passage in Scripture which explicitly speaks about where babies go who die in infancy is 2 Samuel 12. In the context of this passage, David committed adultery with Bathsheba. The prophet, Nathan, boldly confronts David about his adultery and tells him that the child that Bathsheba has conceived will die. As a result of the confrontation, David confesses his sin, puts on sackcloth and ashes, fasts, and mourns the fact that he will lose his child. When David receives news that the child has died, he quits mourning and fasting and changes his clothing. The prophet, Nathan, comes to David and asks him why he quit mourning the loss of his son.
David replies, "While the child was still alive, I fasted and wept; for I said, 'Who knows, the LORD may be gracious to me, that the child may live.' But now he has died; why should I fast? Can I bring him back again? I will go to him, but he will not return to me (2 Sam. 12:22-23)." The text seems to imply that the child went to Heaven since David says, "I will go to him, but he will not return to me"; and elsewhere Scripture indicates that David went to Heaven (Ps. 16:10-11, Heb. 11:32-33).
Third, Scripture may allude to an age of accountability in Isaiah 7:15 which speaks of a child who "will eat curds and honey at the time he knows enough to refuse evil and choose good." If a child dies before this "time," it would seem that he or she would go to Heaven.
It is difficult to be dogmatic about this issue, but we can rest in the fact that God is holy, righteous, and just. Therefore, whatever God chooses to do with infants will be best for them.1
- 1. References: Norman Geisler, "Infants, Salvation of," in The Baker Encyclopedia of Christian Apologetics, Grand Rapids: Baker, 1999, pp. 363-65.