The Catholic Church allows those deprived of the use of reasoning to partake of Confirmation/Chrismation and Communion in the Eastern Catholic Churches. One receives grace from God through the Sacraments, infants and mentally disabled. The Church from ancient times has allowed infants to partake of the Eucharist.
“With milk, then, the Lord’s nutriment, we are nursed directly we are born;
and as soon as we are regenerated, we are honoured by receiving the good news of the hope of rest, even the Jerusalem above, in which it is written that milk and honey fall in showers,
receiving through what is material the pledge of the sacred food.” - St Clement of Alexandria, The Instructor, Book 1, Ch 6
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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 the foregoing prayer, depart. Let the mothers receive their children; let no one have anything against any one; let no one come in hypocrisy; let us stand upright before the Lord with fear and trembling, to offer. When this is done, let the deacons bring the gifts to the bishop at the altar; and let the presbyters stand on his right hand, and on his left, as disciples stand before their Master.
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“And let the people answer: There is One that is holy; there is one Lord, one Jesus Christ, blessed for ever, to the glory of God the Father. Amen. “Glory to God in the highest, and on earth peace, good-will among men. Hosanna to the son of David! Blessed be He that cometh in the name of the Lord,” being the Lord God who appeared to us, “Hosanna in the highest.” And after that,
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. And let the bishop give the oblation, saying, The body of Christ; and let him that receiveth say, Amen. And let the deacon take the cup; and when he gives it, say, The blood of Christ, the cup of life; and let him that drinketh say, Amen.” - Apostolic Constitutions, Book 8, Ch 12-13
“Those who say that infancy has nothing in it for Jesus to save, are denying that Christ is Jesus for all believing infants. Those, I repeat, who say that infancy has nothing in it for Jesus to save, are saying nothing else than that for believing infants, infants that is who have been baptized in Christ, Christ the Lord is not Jesus. After all, what is Jesus? Jesus means Savior. Jesus is the Savior. Those whom he doesn’t save, having nothing to save in them, well for them he isn’t Jesus. Well now, if you can tolerate the idea that Christ is not Jesus for some persons who have been baptized, then I’m not sure your faith can be recognized as according with the sound rule. Yes,
they’re infants, but they are his members. They’re infants, but they receive his sacraments. They are infants, but they share in his table, in order to have life in themselves.” - St Augustine of Hippo, Sermon 174
“And what else do they say who call the sacrament of the Lord’s Supper life, than that which is written: “I am the living bread which came down from heaven;” and “The bread that I shall give is my flesh, for the life of the world;” and “Except ye eat the flesh of the Son of man, and drink His blood, ye shall have no life in you?”
If, therefore, as so many and such divine witnesses agree, neither salvation nor eternal life can be hoped for by any man without baptism and the Lord’s body and blood, it is vain to promise these blessings to infants without them. Moreover, if it be only sins that separate man from salvation and eternal life, there is nothing else in infants which these sacraments can be the means of removing, but the guilt of sin…” - St Augustine of Hippo, On the Forgiveness of Sins and the Baptism of Infants, Book 1, Ch 33
"Question XVII [to Pope St Leo of Rome]. Concerning those who have been captured by the enemy and are not aware whether they have been baptized but know they were several times taken to church by their parents, whether they can or ought to be baptized when they come back to Roman territory?
“[Pope St Leo of Rome’s]Reply.
Those who can remember that they used to go to church with their parents can remember whether they received what used to be given to their parents. But if this also has escaped their memory, it seems that that must be bestowed on them which is not known to have been bestowed because there can be no presumptuous rashness where the most loyal carefulness has been exercised.” - Pope St Leo of Rome, Letter CLXVII, Ch 3
