Whom does Jesus refer to as 'infants' at Luke 10:21?

My Perspective

My view is that "infants" refers to the true disciples that Jesus had.

It is commonplace to let Scripture interpret Scripture. Ergo, I will provide a few verses to support my view.

Firstly, John says that whoever believes and accepts Jesus is given the privilege of becoming a child of God.

¹²Yet to all who did receive him, to those who believed in his name, he gave the right to become children of God— ¹³children born not of natural descent, nor of human decision or a husband’s will, but born of God. John 1:12-13 NIV

So we learn here that it is whoever that believes that become like a child.

¹⁶But Jesus called the children to him and said, “Let the little children come to me, and do not hinder them, for the kingdom of God belongs to such as these. ¹⁷Truly I tell you, anyone who will not receive the kingdom of God like a little child will never enter it.” Luke 18:16-17 NIV

Also, those who wish to get into the kingdom must accept the kingdom like a little child as you can see from the verse. So the servants/subjects/citizens of the kingdom are like little children. That means since the disciples of the kingdom are like little children, they could be referred to as such in metaphor. Moreover, there is one especially damning (pun not intended) evidence to the fact that the "infants" being spoken of here are the true disciples of Jesus.

⁴²And if anyone gives even a cup of cold water to one of these little ones who is my disciple, truly I tell you, that person will certainly not lose their reward.” Matthew 10:42 NIV

The context here is that Jesus is talking about the persecution that the disciples will face in their life when they preach the gospel to the nations. So he directly refers to a disciple as "one of these little ones", which sounds extremely close to "infants" (probably a result of translation differences).

Catholic Church's Perspective

So onto the second part of your question, I believe that the Catholic Church would agree with me. If not because of my reasoning and the context of the passage referring to his disciples and his ministry, then because that one of their own venerated Saints said

“Whosoever is a LITTLE ONE, let him come to me.’ (Proverbs 9:4) And so I succeeded. I felt I had found what I was looking for. But, wanting to know, O my God, what You would do to the very little one who answered Your call, I continued my search and this is what I discovered: ‘As one whom a mother caresses, so will I comfort you; you shall be carried at the breasts, and upon the knees they shall caress you.’ (Isaiah 66: 13,12) Ah! Never did words more tender and more melodious come to give joy to my soul. The elevator which must raise me to heaven is Your arms, O Jesus! And for this I had no need to grow up, but rather I had to remain little and become this more and more.” - St Therese of Lisieux

The source of that quote is found here.

Since a saint was referred to as a little one in her own words, she must have been taught or taught that a disciple/believer was to be like a little one, and therefore must have perceived the verse in Luke 10:21 as a reference to the believers and disciples of Jesus.

As of what exactly they teach on this, there is always the chance to ask Catholic priests either in person and even online! I'm sure they would agree with something along the lines of the answer given under My Perspective. Thanks for reading and I hope this answers your question!

The position of the Catholic Church does not only have to be found in the CCC or in papal documents, but also in the Tradition, in this case, specifically the Fathers. Cornelius a Lapide, though not a Father, taught at the Pontifical Gregorian University, and by that fact and by his eminence in learning his exegesis has considerable weight.

Cornelius a Lapide:

In that hour Jesus rejoiced in spirit (Spiritu Sancto, Vulgate), because the Holy Spirit had, according to His promise, granted the disciples, though weak and unlearned men, the power of working wonders, and had thus led others to believe in Christ and to glorify God. And hast revealed them unto babes, i.e. that thou hast revealed to my humble and unlearned disciples the truth, so that they might acknowledge Thee, the one true God, and Me whom Thou hast sent, and might be predestinated to eternal life; and that many others also, whom they have healed of their diseases, and from whom they have cast out devils, might be brought to the knowledge of God, and believe to the salvation of their soul.

St. Clement of Alexandria:

After we have repented of our sins, renounced our wickedness, and have been purified by baptism, we turn back to the eternal light, as children to their Father. “Rejoicing in the spirit, Jesus said, ‘I praise you, Father, God of heaven and earth, that you have hidden these things from the wise and prudent, and revealed them to little ones.’ ” The Educator and Teacher is naming us “little ones,” meaning that we are more ready for salvation than the worldly wise who, believing themselves wise, have blinded their own eyes. He cries out in joy and in great delight, as if attuning himself to the spirit of the little ones, “Yes, Father, for such was your good pleasure.” That is why he has revealed to little ones what has been hid from the wise and prudent of this world.

St. Bede the Venerable:

Confessing does not always signify penitence, but also thanks airing, as is frequently found in the Psalms. He therefore gives thanks that He had revealed to the Apostles as to babes the sacraments of His coming, of which the Scribes and Pharisees were ignorant, who think themselves wise, and are prudent in their own sight. To the wise and prudent then He opposed not the dull and foolish, but babes; that is, the humble, to show that He condemned pride, not quickness of mind. Orby the words, All things are delivered to me, He means not the elements of the world, but those babes to whom by the Spirit the Father made known the Sacraments of His Son; and in whose salvation when He here spoke He was rejoicing

All these can be found on Catena