What do Protestant churches teach about the fate of deceased infants?

As others have mentioned, there are many Protestant denominations and a wide spectrum of diversity within those deominations. The real issue boils down to Calvinist denominations and Arminian or Non-Calvinist denominations.

The following quote is from Timf, who summarized it very accurately in his answer:

"Most churches would teach that infants who die before an age of accountability would be saved. This view would be derived from verses that testify to the mercy and goodness of God. Even without verses that spell out the specifics and mechanism by which and why this happens, most would trust in the mercy and goodness of God."

I can say with certainty that this is the position of Southern Baptists and most Freewill Baptists, Nazarenes, Bible Methodist, Church of God, Assembly of God, Holiness churches and most Pentecostal churches as well as most Evangelical Free Church of America - particularly the ones where the leaders are not Calvinist.

This issue here is really the same exact issue that relates to people born with severe mental disabilities and is another problem for the Calvinists. In one PCA church it was the teaching that all aborted babies go to hell, but some PCA churches teach that babies who are born to Christian parents must be elect, so these babies that die in infancy go to heaven- a huge stretch and not supported by scripture.

Most Protestant churches teach the principle of Age of Accountability, and this is based on at least 5 scriptures.

• Matthew 19:14 English Standard Version 14 but Jesus said, “Let the little children come to me and do not hinder them, for to such belongs the kingdom of heaven.”

• 2 Samuel 12:23 "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." When David's child died and he was comforted knowing that he would see him again in heaven.

• Romans 5:13 "for sin indeed was in the world before the law was given, but sin is not counted where there is no law."

• Romans 4:15 "For the law brings wrath, but where there is no law there is no transgression."

In addition to these, Protestants also use the passages in the Old Testament about children who are not old enough to go to war and the concept of Bar Mitzvah - that a boy or girl comes of age at age 13.

It should be noted that this same Biblical principle of age of accountability also applies to the millions born with cerebral palsy, severe autism, and other mental illness, who are not capable of understanding the law or the 10 commandments, and sin/ atonement or repentance.

The scripture references about the fate of unbaptized children of a Christian follow.

For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband: else were your children unclean; but now are they holy. 1 Cor 7:14

"Holy" means "Holiness, Holy, Holily:

akin to A, Nos. 1 and 2, which are from the same root as hagnos (found in hazo, "to venerate"), fundamentally signifies "separated" (among the Greeks, dedicated to the gods), and hence, in Scripture in its moral and spiritual significance, separated from sin and therefore consecrated to God, sacred."

Moreover, Paul isn't making something up, but using this principle.

For if the firstfruit be holy, the lump is also holy: and if the root be holy, so are the branches. Romans 11:16

So, if a parent is holy (saved, born-again), the lump or branches (children) are too.

The fate of children of the unsaved is a different topic.

An important and probably decisive principle of the Bible is not only found in the fact that 1. the age of 20 is overproportionally often mentioned in the Bible (32 times), that 2. most of the kings started their office at or shortly after the Age of Accountability of 20 years, but 3. especially in Num 14:29-33, where God excluded children up to the age of 19 years from the condemnation of their respective tribes:

... in this desert your corpses will fall, and all your counted ones, according to all your number, from twenty years old and above who grumbled against me. [...] But your little children, whom you said would be plunder, I will bring them, and they will know the land that you rejected.

God punished here the people of the lying spies, but intentionally excluded their children.

The parallel passage is found in Deu 1:39 - with the very important addition that those children do not know good or bad:

And your little children, who you thought shall become plunder, and your sons, who do not today know good or bad, shall themselves go there [the Promised Land which can be paralleled to our future Promised Land], and I will give it to them, and they shall take possession of it.

If God excluded in 1446 BC children under the age of 20 from condemnation, then He will do so especially after the First Coming of Jesus Christ. It would be abstruse to assume the contrary.

Furthermore, children are described as 'innocent' in Jer 19:4-5:

... they have filled up this place with the blood of the innocent, and they have built the high places of Baal, to burn their children in the fire ...

1Cor 7:14 saying 'they are holy' and Mat 19:14 stating 'to such belongs the Kingdom of Heaven' make it clear that all children of true believers who will have died until the age of 19, will be part of the New Jerusalem. Meanwhile, children of unbelieving parents who will have died until the age of 19 will form those nations that serve the New Jerusalem.

Isa 60:14-20 ... And the children of those who oppressed you shall come to you bending low ... [...] And you shall call your walls Salvation [...] The sun shall no longer be your light by day ...

(See also Rev 21:24-27, Rev 22:1-2, Hos 2:18, Mic 4:1-5 and Luk 19:17-19 for more details about the surrounding nations, a topic commonly overlooked in eschatology. All unbelievers not found in the Book of Life will be in hell, but their children who will have died until the age of 19 will form the nations outside the New Jerusalem).

Hope that clarifies the question which is still very relevant.

What do Protestant churches teach about the fate of deceased infants?

Although this subject can be woven into the various doctrines of infant baptism, most Protestants would look to a biblical basis for their doctrine. The only verse that comes close to describing a specific teaching on this describes David’s reaction to the loss of his son;

2 Samuel 12:23 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.

Here there is a degree of uncertainty if David is describing death and the grave or the resurrected state.

Without a specific verse describing a clear and specific doctrine, we enter the arena of derived doctrine. This is always a little tricky and one should tred carefully.

We know that because of sin everything that lives must die.

Romans 6:23 For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.

We know that after death comes judgment;

Hebrews 9:27 And as it is appointed unto men once to die, but after this the judgment:

The question becomes what judgment is made of those who were too young to understand what they did (what has been called the age of accountability). We do get an idea that there are circumstances where God withholds judgment;

Acts 17:29-30 Forasmuch then as we are the offspring of God, we ought not to think that the Godhead is like unto gold, or silver, or stone, graven by art and man's device. And the times of this ignorance God winked at; but now commandeth all men every where to repent:

We do know that God judges those who reject the revelation of him in nature;

Romans 1:20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse:

Here we get an idea that if the eternal power and Godhead were not discernible (which would be the case for infants) that there might be an “excuse”.

Some advance the idea that there are those “elect” from the womb who are saved by virtue of their election. These often cite David as an example of this condition.

Psalm 22:9-10 But thou art he that took me out of the womb: thou didst make me hope when I was upon my mother's breasts. I was cast upon thee from the womb: thou art my God from my mother's belly.

These would view that some are saved by virtue of their election. However this view implies the condemnation of those who are not elect. This view gains support also from David;

Psalm 58:3 The wicked are estranged from the womb: they go astray as soon as they be born, speaking lies.

There are basically three views;

1. All go to hell. In this view because of the pervasive nature of original sin all infants are guilty and worthy of condemnation. Some might be saved by baptism or become old enough to understand their need of a Savior and trust in Jesus but otherwise they have no hope. This view is somewhat modified if one considers that hell might not be as eternal as one thinks (the definition of the Greek “aion” can be quite variable) and that judgment is proportional to works;

Revelation 20:13 And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works.

2. Some are saved. In this view there is a reason for some infants to be saved (such as election). However, others are still destined for hell.

3. All are saved. In this view judgment is not made for those who were unable to be responsible. This view gains support from Jesus;

John 9:41 Jesus said unto them, If ye were blind, ye should have no sin: but now ye say, We see; therefore your sin remaineth.

Most churches would teach that infants who die before an age of accountability would be saved. This view would be derived from verses that testify to the mercy and goodness of God. Even without verses that spell out the specifics and mechanism by which and why this happens, most would trust in the mercy and goodness of God.