Well, I’m Lutheran, so I don’t believe in an age of accountability. Here’s what we believe: Salvation, from beginning to end, is from God. But damnation, from beginning to end, is from man. This is a holy mystery that is apprehended through faith, which is given by the Holy Spirit, through the means of the Gospel.
Scriptures say that we are by nature children of wrath; brought forth in iniquity, conceived in sin and dead in sin. That is, we are sinners not because we sin, but rather, we sin because we’re sinners. Again, the Word of God says that no one is righteous before God - not even one. So, all are in need of God’s grace - a Saviour. What is born of the flesh must be born of the Spirit. This is true for all, regardless of age.
Now, it’s my belief that God’s grace may extend to the little ones who were not baptised, for we know that God is good and righteous, saying "Let the little children come to me", and while baptism is ordinarily the means of grace, that does not mean that God is bound by His own means. Quite simply, we can take comfort in that whatever God judges, it is good and right, and it’s not something we need to speculate on or worry about. Our concern should be to uphold the purity of God’s Law and Gospel, that is, the full council of God’s Word. And this means proclaiming the good news of the forgiveness of sins to the repentant, but warning to the unrepentant. That is, we must proclaim that there is salvation in Christ, but damnation for all who reject God's grace. When Christ says that the unbeliever will be condemned, it really means condemned, and we have to hold fast to the Word of Christ.