The Roman priest is bound to celebrate the Mass according to the Latin form.
In canon law, “whatever applies to the whole, applies to every part-of the whole.”
Since the priest is bound to follow the Latin laws/rules for the whole of the Mass, he is also bound to follow the Latin form for every individual part of the Mass. The Latin code is clear that the priest cannot administer Communion to infants.
Can. 913 §1. 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.
What that means is that you do not have a “right” to insist that the priest administer Communion to your daughter.
While it is true that there is no canon law that says “when in Rome, do as the Romans do”–that does not mean that somehow there IS a law that says “when in Rome, you may do as the Byzantines do”
Every liturgical (or para-liturgical to use the Eastern vocab.) act must follow the ritual and the rules of that specific Church sui iuris which celebrates it.
Can. 846 §1. In celebrating the sacraments the liturgical books approved by competent authority are to be observed faithfully; accordingly, no one is to add, omit, or alter anything in them on one’s own authority.
§2. The minister is to celebrate the sacraments according to the minister’s own rite.
#2 is what’s important here. The Latin priest is bound to follow the ritual and laws of the Latin Rite Mass, and the laws that govern that Mass prohibit him from administering Communion to infants. If he visits an Eastern parish and joins in the Divine Liturgy, then he would be bound to observe the Eastern form—but that’s not the case here.
Again, whatever applies to the whole applies to every part. A Latin priest is bound to celebrate the entire Mass according to the Latin Rite usage–and that includes the rules for Communion.
An Eastern Catholic does not have a right to insist that the Latin priest at Mass administer Communion to an infant any more than there is a “right” to insist that the Trisagion be used as a form of the Kyrie in the Latin Mass just because one or more members of the congregation are Eastern Catholic.
Conclusion:
You do not have any “right” to insist that the Latin priest administer Communion to your infant daughter when you attend a Latin Rite Mass. There is no such right because you cannot compel the Latin priest to violate the laws that prohibit him from doing so.
Regardless of what you’ve already read that’s been posted here, you do not have any right to insist that the Latin Rite priest violate his own obligations under canon 846.2
You cannot impose this on him.
Pastoral response:
First, talk to the (Latin) priest and explain things to him. Don’t go waving some pamphlet in his face and insist that he “must” do what he already knows he cannot do.
The law prohibiting the Latin priest from administering Communion to infants is a disciplinary law of the Church (certainly not Divine Law). As such, the local bishop can dispense him from it. Personally, I don’t think this would need to be anything formal, just a simple verbal dispensation would suffice. I also personally think that such a dispensation would be readily given if the request is reasonably made.
Now the important thing for you to do is to put him into a position where he is willing to request that dispensation.
Waving pamphlets under his nose, threatening to report him to Rome, and above all insisting that you know more than he does about this because you “read something on the internet” or any other kind of confrontational behavior will not help the situation. In fact, it will only make matters worse because you will be essentially telling the Latin Rite priest that you think he’s been over-ruled by an internet forum. Believe me, this will make things worse. This strategy will bring you nothing but headaches.
If you present this to him in a non-confrontational way, he may just see fit to contact the bishop (or the vicar general, or even the local dean if the bishop has delegated his deans to grant this kind of dispensation–some have) first request, and then receive a dispensation from his obligation under canon 913 (no Communion to infants). Remember, it’s a dispensation from the priest’s obligation—not a dispensation for your daughter.
If you go about this the right way, you just might find that the end-result is exactly what you were hoping to achieve.
If you go about it the wrong way, meaning that you try to tell the priest that he has been over-ruled by an internet forum, you will only make things worse.
I wish you the best.