You are right that the Roman Catholic church does not commune infants. Here is a small quote from this website
Who Can Receive Communion? | Catholic Answers
"Catholics and Communion:
The Church sets out specific guidelines regarding how we should prepare ourselves to receive the Lord’s body and blood in Communion. To receive Communion worthily, you must be in a state of grace, have made a good confession since your last mortal sin, believe in transubstantiation, observe the Eucharistic fast, and, finally, not be under an ecclesiastical censure such as excommunication.
First, you must be in a state of grace. "Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord. Let a man examine himself, and so eat of the bread and drink of the cup" (1 Cor. 11:27–28). This is an absolute requirement which can never be dispensed. To receive the Eucharist without sanctifying grace in your soul profanes the Eucharist in the most grievous manner.
A mortal sin is any sin whose matter is grave and which has been committed willfully and with knowledge of its seriousness. Grave matter includes, but is not limited to, murder, receiving or participating in an abortion, homosexual acts, having sexual intercourse outside of marriage or in an invalid marriage, and deliberately engaging in impure thoughts (Matt. 5:28–29). Scripture contains lists of mortal sins (for example, 1 Cor. 6:9–10 and Gal. 5:19–21). For further information on what constitutes a mortal sin, see the Catechism of the Catholic Church.
Out of habit and out of fear of what those around them will think if they do not receive Communion, some Catholics, in a state of mortal sin, choose to go forward and offend God rather than stay in the pew while others receive the Eucharist. The Church’s ancient teaching on this particular matter is expressed in the Didache, an early Christian document written around A.D. 70, which states: "Whosoever is holy [i.e., in a state of sanctifying grace], let him approach. Whosoever is not, let him repent" (Didache 10).
Second, you must have been to confession since your last mortal sin. The Didache witnesses to this practice of the early Church. "But first make confession of your faults, so that your sacrifice may be a pure one" (Didache 14).
The 1983 Code of Canon Law indicates that the same requirement applies today. "A person who is conscious of a grave sin is not to . . . receive the body of the Lord without prior sacramental confession unless a grave reason is present and there is no opportunity of confessing; in this case the person is to be mindful of the obligation to make an act of perfect contrition, including the intention of confessing as soon as possible" (CIC 916)."
It goes on and on but I think this covers it well.