For parents who have lost a child, the gospel of Jesus Christ is a great comfort. God is a Father, and Jesus Christ is the Son of God. When the Son of God died on the cross, the Father experienced exactly what it feels like to lose a beloved child.
Regarding what happens to a child after they die, and whether or not they go to Heaven, the most common Scripture given to answer that question is from the Old Testament. There, David is the father of a beloved child who died.
2 Samuel 12:15–23 says:
And the LORD afflicted the child that Uriah’s wife bore to David, and he became sick. David therefore sought God on behalf of the child. And David fasted and went in and lay all night on the ground. And the elders of his house stood beside him, to raise him from the ground, but he would not, nor did he eat food with them. On the seventh day the child died. And the servants of David were afraid to tell him that the child was dead, for they said, “Behold, while the child was yet alive, we spoke to him, and he did not listen to us. How then can we say to him the child is dead? He may do himself some harm.” But when David saw that his servants were whispering together, David understood that the child was dead. And David said to his servants, “Is the child dead?” They said, “He is dead.” Then David arose from the earth and washed and anointed himself and changed his clothes. And he went into the house of the LORD and worshiped. He then went to his own house. And when he asked, they set food before him, and he ate. Then his servants said to him, “What is this thing that you have done? You fasted and wept for the child while he was alive; but when the child died, you arose and ate food.” He said, “While the child was still alive, I fasted and wept, for I said, ‘Who knows whether the LORD will be gracious to me, that the child may live?’ But now he is dead. Why should I fast? Can I bring him back again? I shall go to him, but he will not return to me.”
David had hope for his deceased child on the other side of death, and so should we.
The language of salvation in the Bible is that God is a Father and to become a Christian is to be adopted into His family as His child. This is how everyone is saved, young and old. Ultimately, God the Father determines which children He will spiritually adopt into His family. This is his decision. It is not the decision of parents who have sent their children on to him, nor the theologians who try and give a guarantee to grieving parents.
The Father decides. And, that is good news.
The same Father who sought me, saved me, and sealed me is the same Father I am trusting to do what is right and best with the baby we lost to miscarriage. I trust Him. I trust Him fully. I trust Him completely. I trust Him for myself. I trust Him for my family.
On the question of whether or not a deceased little one goes to Heaven, I find the doctrines of predestination and election to be greatly comforting. I cannot predestine my child by constructing a theology of them being saved by virtue of being born into a covenant family. I cannot predestine them by inventing an age of accountability. I cannot predestine them by having them sprinkled and calling it baptism when they are little. My job is not to predestine, but rather to praise the One who does.
I am a father who worships a Father. My Father seeks spiritual children who are unable to seek or find him because of their spiritual deadness—but He finds them. I am a father who worships a Father who brings life where there is death. I am a father who worships a Father that has given me his Father’s heart for my children and so I know my Father’s heart.
And while I do not have a clear promise from Scripture for what happens to little ones who pass, including our own miscarried child that I think was a baby boy, I do trust my Father. I am certain—by faith guided by Scripture and rooted in the character of the Father—that one day in his presence, by his grace, for his glory, I will hug my child while Jesus wipes every tear from my eye and I will weep no more because my Father has taken care of everything and His Son died for my son.