In his decree Quam Singulari, the saint explained his decision:

The pages of the Gospel show clearly how special was that love for children which Christ showed while he was on earth. It was his delight to be in their midst … He embraced them; and He blessed them. At the same time, he was not pleased when they would be driven away by the disciples, whom he rebuked gravely with these words: “Let the little children come to me, and do not hinder them, for of such is the kingdom of God.”

He hoped that this change in discipline would “bring about that children even from their tender years may be united to Jesus Christ, may live His life, and obtain protection from all danger of corruption.” The saintly pope was convinced that by receiving Holy Communion worthily, children would grow in holiness and be protected from sin. These are effects which the Catechism of the Catholic Church teaches in CCC no. 1416.

As long as a child can discern the difference between plain bread and the reality that the consecrated host is truly Jesus under the appearance of bread, she or he can be considered "ready" to receive Holy Communion by their parents and pastor. Sometimes, though, they may discern that the child should wait a little longer – or they may see that a child is ready before the age of 7. Once, when a 4-year-old boy impressed the pope with his clarity and understanding of the Eucharist, Pius X offered the child his first Holy Communion. But these are exceptions, not the norm.

The Code of Canon Law states: "The administration of the Most Holy Eucharist to children requires that they have sufficient knowledge and careful preparation so that they understand the mystery of Christ according to their capacity and are able to receive the body of Christ with faith and devotion. The Most Holy Eucharist, however, can be administered to children in danger of death if they can distinguish the body of Christ from ordinary food and receive communion reverently." (Can. 913)

It is good to keep in mind, though, that the Latin rite of the Catholic Church is only one of 24 different Rites. Each Rite often has its own distinct disciplines and liturgical traditions around the celebration of the sacraments, including the Eucharist.

Many of the Eastern Rites administer the three sacraments of initiation all at once to newborns: Baptism, Confirmation, and then Eucharist – which is the original order used in the early Church. The infant's first Holy Communion is carefully given by means of a few drops of the Precious Blood.

No matter what age a person first receives Holy Communion, the words of Pope St. Pius X apply. He insisted that the reception of Holy Communion is the “shortest and safest way to get to heaven.”