Council of Trent: Session 21
Chapter 3
That Christ whole and entire, and a true Sacrament are received under either species.
It moreover declares, that although, as hath been already said, our Redeemer, in that last supper, instituted, and delivered to the apostles, this sacrament in two species, yet is to be acknowledged, that Christ whole and entire and a true sacrament are received under either species alone; and that therefore, as regards the fruit thereof, they, who receive one species alone, are not defrauded of any grace necessary to salvation.
Chapter 4
That little Children are not bound to sacramental Communion.
Finally, this same holy Synod teaches, that little children, who have not attained to the use of reason, are not by any necessity obliged to the sacramental communion of the Eucharist: forasmuch as, having been regenerated by the laver of baptism, and being incorporated with Christ, they cannot, at that age, lose the grace which they have already acquired of being the sons of God. Not therefore, however, is antiquity to be condemned, if, in some places, it, at one time, observed that custom; for as those most holy Fathers had a probable cause for what they did in respect of their times, so, assuredly, is it to be believed without controversy, that they did this without any necessity thereof unto salvation.
On Communion Under Both Species, and on the Communion of Infants
CANON I.—If any one saith, that, by the precept of God, or, by necessity of salvation, all and each of the faithful of Christ ought to receive both species of the most holy sacrament not consecrating; let him be anathema.
CANON II.—If any one saith, that the holy Catholic Church was not induced, by just causes and reasons, to communicate, under the species of bread only, laymen, and also clerics when not consecrating; let him be anathema.
CANON III.—If any one denieth, that Christ whole and entire—the fountain and author of all graces—is received under the one species of bread; because that—as some falsely assert—He is not received, according to the institution of Christ himself, under both species; let him be anathema.
CANON IV.—If any one saith, that the communion of the Eucharist is necessary for little children, before they have arrived at years of discretion; let him be anathema.
As regards, however, those two articles, proposed on another occasion, but which have not as yet been discussed; to wit, whether the reasons by which the holy Catholic Church was led to communicate, under the one species of bread only, laymen, and also priests when not celebrating, are in such wise to be adhered to, as that on no account is the use of the chalice to be allowed to any one soever; and, whether, in case that, for reasons beseeming and consonant with Christian charity, it appears that the use of the chalice is to be granted to any nation or kingdom, it is to be conceded under certain conditions; and what are those conditions: this same holy Synod reserves the same to another time,—for the earliest opportunity that shall present itself,—to be examined and defined.