Council of Trent: Session XXI, Communion, Chapter IV

CHAPTER IV. 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 th 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.

Translation: J. Waterworth, The Canons and Decrees of the Council of Trent (1848), Hanover Historical Texts Project transcription (1995).