What is the Biblical basis for asserting that infants can have faith in Christ under a Calvinistic framework?

I think John Calvin taught God elects people before the creation of the world. Predestination is the doctrine that God chooses some people but not others, and he chose them before the beginning of the world.

For he chose us in him before the creation of the world to be holy and blameless in his sight (Ephesians 1:4)

If God chooses people to be holy and blameless (i.e. saved) before they are even born, then I think it's fair to argue that infants who are chosen will be holy and blameless.

Personally, I don't think this teaches that all infants are saved. Only those who are chosen are saved. Could God have chosen all infants who die as infants? Yes he could have, but we have no evidence of that.

Calvin puts his own view on the subject most directly in a section of his institutes of religion called “Paedobaptism. Its accordance with the institution of Christ, and the nature of the sign.” In this section he is arguing for the case of infant baptism and one of the arguments from the Anabaptists was that why should you baptize an infant who can’t have faith? Now as Calvin did not think baptism was necessary for salvation, only that he thought it was good to continue the practice, the more serious and important subject of ‘infant election’ is addressed.

Calvin states his belief that elect infants can be justified and in some sense have faith. He denies the supposition that infants can’t have faith. First is asserts a form of the First option, i.e. that infants can be justified within a mystery where we do not really understand how it is that they have faith:

But how, they ask, are infants regenerated, when not possessing a knowledge of either good or evil? We answer, that the work of God, though beyond the reach of our capacity, is not therefore null. Moreover, infants who are to be saved (and that some are saved at this age is certain) must, without question, be previously regenerated by the Lord. For if they bring innate corruption with them from their mother’s womb, they must be purified before they can be admitted into the kingdom of God, into which shall not enter any thing that defileth, (Rev. 21:27.) If they are born sinners, as David and Paul affirm, they must either remain unaccepted and hated by God, or be justified. (Institutes, Vol.4: Part 17)

Calvin does not stop here. He also moves to the Second, i.e., that infants can have faith by the ‘work of the Spirit’ even in the womb, although admittedly this might be very rare:

But to silence this class of objectors, God gave, in the case of John the Baptist, whom he sanctified from his mother’s womb, (Luke 1:15,) a proof of what he might do in others. They gain nothing by the quibble to which they here resort, viz., that this was only once done, and, therefore, it does not forthwith follow that the Lord always acts thus with infants. That is not the mode in which we reason. Our only object is to show, that they unjustly and malignantly confine the power of God within limits, within which it cannot be confined. (Institutes, Vol.4: Part 17)

What I find about Calvin’s argument is not any illogical part but that they are simply thin. I guess as he was only arguing about another point he failed to more thoroughly address the subject. There are two things that make me feel more is required to provide a biblical basis. Two answers still need to be provided. Why is the Bible more or less silent about the subject of the faith of infants and why should we consider that John the Baptist’s sanctification from the womb could have been evidence of faith in Christ?

To answer the first question, ‘Why is the Bible more or less silent about the subject of the faith of infants?’ It is safe to say that where the scripture does not provide light, we are to be content trusting God by faith without clarity. The whole problem over these sorts of subjects is that we seek a systematic theology that answers every question, and then we think we have finally ‘arrived’ at the answer. However there are several subjects that God has not made fully know to us and even when our knowledge is very small we have arrived at the answer only because God has taken us in his hand and we have taking his in trust. The greatness of his mind leaves all our sailing thoughts left behind, but we can trust he loves us and loves all children, whether elect for salvation or damnation. Faith trusts God, like Abraham who was willing to offer up Isaac as a sacrifice knowing that God could raise him from the dead.

Too answer the second question, ‘Why should we consider that John the Baptist’s sanctification from the womb could have been evidence of faith in Christ?’ We must acknowledge that the scripture is mostly silent on this issue and the few places where the womb is talked about are few and could be seen as merely marking out God’s calling on the individual.

Here are some few examples of something happening in the womb that seems to be an interaction with the Spirit:

The children struggled together within her, and she said, “If it is thus, why is this happening to me?” So she went to inquire of the LORD. (Genesis 25:22)

This could be understood as simply a unlikely movement of infants which Rebekah superstitiously considered as a bad omen, but there are many coincidental things about Jacob and Esau which the scriptures lift up almost centrally to view the subject of predestination with, therefore it could also be a mark that the Spirit of God was moving on Jacob. We can’t help but notice that this struggling seems to have also resulted in the outcome of Jacob holding Esau’s heel as he was already seeking the birthright from which Messiah would come. Yes these are all seeming coincidences but even later Hosea the prophet matches Jacob’s wrestling in the womb to his later wrestling with Christ for the blessing (Hos 12:3)

Sometimes when the Bible mentions God’s calling from the womb there is no mention of anything actually occurring in the womb so it can be inferred that this is simply a way of describing and eternal calling on one’s life. For example Paul used this idea in Galatians 1:15. Samson was ‘dedicated to God’ from his Mother’s womb (Judges 16:17). Jeremiah was ‘set apart’ in eth womb (Jeremiah 1:5), etc. However in the case of John the Baptists we again, like Jacob have mention about something literally happening in the womb.

First John is said to be ‘filled with the Spirit’, even in the womb:

for he will be great before the Lord. And he must not drink wine or strong drink, and he will be filled with the Holy Spirit, even from his mother’s womb. (Luke 1:15, ESV)

But not only so, John literally responds to Jesus in the womb:

And when Elizabeth heard the greeting of Mary, the baby leaped in her womb. (Luke 1:41, ESV)

Yes, it could be that again just a coincidental movement of the baby occurred under God’s miraculous guidance to create the ‘impression’ that John was reacting to the nearness of the Christ, or he was actually being filled with the Spirit in the womb and could not help but react literally to Christ. It is the second possibility that Calvin argues as a sample case, to ‘partially pierce the veil of the mystery’ of election, where infants are concerned.

It is the view of some of the most eminent Calvinists that all those who die in infancy go to Heaven, including Charles Spurgeon and John Gill.

But they are not saved because they did not reject the Gospel: souls are lost not because they reject the Gospel but because they are sinners. True, only receiving the Gospel can save them, but they are lost already before they ever come close to the Gospel. All men in every remote island and mountain far away from the sound of the Gospel are lost, totally lost, and will remain lost till the Gospel ventures into their neighbourhood, is preached to them, and they receive it.

The usual reason for advocating that infants dying in infancy are saved is that they have never deliberately sinned, and so they fall under the grace of God as it is given in Jesus, Jesus death being effective to redeem their sinful nature, Jesus being their federal head.

Also, Calvinists sometimes assert that faith is not the issue in the case of infants, since they have no ability to declare it, and no ability to have it. What is important is whether they are regenerate. It is God who regenerates the soul. For adults, regeneration and faith come together, and faith in Christ is the sign their soul is regenerate. For infants, they may be regenerate but neither they nor others are conscious of any faith.

The Calvinist Charles Spurgeon preached a sermon "Infant Salvation" which argues that all those dying in infancy are saved, which you can read here:-

https://www.spurgeon.org/resource-library/sermons/infant-salvation#flipbook/

or here:-

https://www.metropolitantabernacle.org/Christian-Article/Infant-Salvation-Charles-Spurgeon/Sword-and-Trowel-Magazine

This second link proves that some Calvinists today still hold to this belief. For me, it is quite monstrous to think that God, who is love, would send souls to everlasting Hell even though they died in infancy. I think it deeply insulting to our Heavenly Father and our Saviour.