It doesn’t change the fact that at a Roman Mass, the code that applies is the Latin code of 1983. It’s rather simple (yet, so is the solution).
It applies to the pastor, but the Eastern Catholics are visitors to the parish, and particular law does not bind them.
They are subject to the Code of Canon Law for the Eastern Churches and thus may freely and legally seek the Sacraments, including the infants.
Father, I don’t say this very often to priests, but you are mistaken.
I am fortunate enough to live in an area with large numbers of Eastern Catholics ( heck Sacred Heart Seminary trains priests for the Chaldean Church as well as the Roman one
The Catholic School I went to had a Rutherian parish in the same town that was a ‘feeder’ parish into our school. About a 1/3 of my class was Eastern between them and the Chaldeans(as yes, the Eastern Kindergarteners went up for Communion at school Masses.
What I would recommend to you is that you consult your Chancellory with this question for verification.
To the OP, I would make a similar counsel, to contact the Bishop’s office for your Eparchy. They will have experience with providing the necessary proofs to Roman clergy, especially if the Eparchy covers areas with little Eastern presence.