You will fine below references from the Early Church regrading both infant baptism and providing Holy Communion to infants. With just a little research you will learn that the practice  / theology of denying Holy Communion to infants did not really become prevalent in the west until the 12th century and in particular after the Council of Trent and the Roman Doctrine of Transubstantiation which is a teaching of the Council of Trent. This entire council for the most part is rejected by Old Catholics. I ask you to consider:

Baptism

Baptism is the Christian equivalent of circumcision or "the circumcision of Christ," as Paul states: "In him you were also circumcised . . . with the circumcision of Christ, having been buried with him in baptism and raised with him through your faith in the power of God, who raised him from the dead" (Col. 2:11-12). Thus, like circumcision, baptism can be given to children as well as adults. The difference is that circumcision was powerless to save (Gal. 5:6, 6:15), but "Baptism . . . now saves you" (1 Pet. 3:21).

The Church Fathers taught the practice of infant baptism and declared it to be of apostolic origin. In fact, a council held in the 250s discussed the question of whether an infant should be baptized on the eighth day after birth (see quotation from Cyprian, below). The only reason one would even discuss this is because one recognized baptism as the Christian equivalent of circumcision, which was given on the eighth day after birth (Lev. 12:2-3).

Cyprian of Carthage

"As to what pertains to the case of infants: You [Fidus] said that they ought not to be baptized within the second or third day after their birth, that the old law of circumcision must be taken into consideration, and that you did not think that one should be baptized and sanctified within the eighth day after his birth. In our council it seemed to us far otherwise. No one agreed to the course which you thought should be taken. Rather, we all judge that the mercy and grace of God ought to be denied to no man born" (Letters 64:2 [A.D. 253]).

The Apostolic Tradition 21:16 [A.D. 215).

"Where there is no scarcity of water the stream shall flow through the baptismal font or pour into it from above; but if water is scarce, whether on a constant condition or on occasion, then use whatever water is available. Let them remove their clothing. Baptize first the children, and if they can speak for themselves let them do so. Otherwise, let their parents or other relatives speak for them"

Paedocommunion – Infants Receiving Holy Communion

Now let’s look at how the Early Church determined who was worthy to receive the Body and Blood of Christ in the Holy Eucharist. With only minimal research we will learn the practice of Infants Receiving Holy Communion was customary practice in both the churches of the East and West until well into the 12th century. I have provided several references below for your review.

If as evidence suggests, paedocommunion (providing Holy Communion to infants) was the customary practice of the church in ancient days, then why do we not practice it today in the Churhc of the West / Roman Catholic?

The doctrine of transubstantiation and the fear that infants and children might spill the wine and thereby profane the actual body and blood of the Lord appears to have been the primary reason for this discontinuance, AND Holy Communion had become associated with reconciliation rather than baptism which is contrary to the faith of the undivided Church.

It is clear in the Early Church and still in the Eastern Orthodox that Baptism is tied to Holy Communion not reconciliation or “understanding” as taught by the current Roman theologians. So, in the end the questions become not who is justified by some means as measured by a denomination. But who is validly baptized into the Body of Christ – The Church?

In the Eastern Church only those immersed into the water according to the Eastern Rite are validly baptized and therefore “circumcised’ into the Body of Christ. So only those who are validly baptized (Orthodox) may partake of Holy Communion. And the Sacrament is given to all children, even infants who are baptized.

The Western Church accepts as valid all those baptized by proper intent and form, However the Roman Church will not allow those who they deem to be validly baptized to partake of Holy Communion until they are properly educated to “understand” the Sacrament and reconciled.

Given we are “western” in both practice and theology we accept all those baptized in the proper intent. However, since we base our theology in the teachings of the undivided church we allow all baptized to receive Holy Communion physical age of the baptized is no indication of spiritual age.

Is our communion open or closed? It is both. Open to all validly baptized into Christ and closed to those not yet baptized.

Didache Chapter 9. The Thanksgiving (Eucharist)

But let no one eat or drink of your Thanksgiving (Eucharist), but they who have been baptized into the name of the Lord; for concerning this also the Lord has said, Give not that which is holy to the dogs. Matthew 7:6

Clement of Alexandria

“As soon as we are regenerated (baptized – my words) we are honoured by receiving the good news of the hope of rest. . . receiving through what is material the pledge of the sacred food.” The Instructor, Ch. VI”

Apostolic Constitutions

“Let none of the catechumens, let none of the hearers, let none of the unbelievers, let none of the heterodox, stay here. You who have prayed for the foregoing prayer, depart. Let the mothers receive [or, take] their children; let no one have anything against anyone; let no one come in hypocrisy; let us stand upright before the Lord with fear and trembling, to offer.”

Constitutions of the Holy Apostles, 8.2.12

. . . . let the bishop partake, then the presbyters, and deacons, and sub-deacons, and the readers, and the singers, and the ascetics; and then of the women, the deaconesses, and the virgins, and the widows; then the children; and then all the people in order, with reverence and godly fear, without tumult. Constitutions of the Holy Apostles, 8.2.13

Augustine

They are infants, but they receive His sacraments. They are infants, but they share in His table, in order to have life in themselves. Works, Vol. 5, Sermon 174:7

Dionysius. The Ecclesiastical Hierarchy,

"The fact that children not yet able to understand divine things become recipients of the holy rebirth in God [baptism] and the most sacred symbols of the supremely divine Communion seems, as you say, to merit the legitimate ridicule of the profane, for it is as though the bishops teach divine things to those who cannot hear, and in vain hand down the sacred traditions to those who do not understand.... not all divine things can be comprehended by our intelligence, but many things unknown by us have reasons worthy of their divine character that escape us, but are understood by the superior orders. Many things are beyond even the most sublime beings and are known distinctly only by the all-wise God, the Source of wisdom. Nevertheless, we affirm on this matter what our godlike instructors, initiated in ancient tradition, have transmitted to us.

"They assert, and it is the truth, that infants brought up according to sacred law will contract a habit of holiness, be guarded from all error, and be inexperienced in an evil life. When our godly leaders arrived at this conclusion, they decided to receive infants in this holy manner: on condition that the physical parents of the child presented confide the child to someone of the initiated in divine things who is a good teacher...

Council of Macon - 585

Ordered that on Wednesdays and Fridays the infants and children of the church should be brought back to the church where they "should receive the remains of the sacrifices."

Council of Toledo - 675

"The sick who found themselves unable to swallow the Eucharist, and others who had failed to swallow it 'in times of infancy,' did not fall under the censure of the first council of Toledo (can. 14), against those who having received did not consume it (can. 11)."41