The kids will have no problem learning it; they are maleable. It’s always the adults that cause the issue. I taught the seasonal Marian antiphons to our school kids four years ago and half the kids had them memorized, and I even had one mother tell me that her kids would sing the salve Regina by wrote while playing together in the back yard. Perhaps that’s one route in: seasonal marian antiphons; you can sing them at the end of all school mass, and then hopefully they will hear them every week (or more).

Assign the children to sing for Maundy Thursday. They'll become convinced that they're doing something important (which they are) and they'll not want to go back to kiddy music for Mass ever again.

Mind you, if the ars celebrandi in a parish is, shall I say "weak" or "unsupportive" of such a goal, even musicians can't work miracles. So,.... first piece of advice: make sure that the environment into which you introduce chant makes sense.

I was, once upon a time, giving a conference on "how not to look and feel like a foreigner at the TLM" to a group of newcomers, at their request. One mom asked me, "So, if what you say is correct, why do people hold hands at the Our Father".... to which I replied that there were two possible answers: if you wanted to find out why people weren't following the rubrics, you should ask those people, not someone who knew they shouldn't be behaving that way; and Original Sin.

https://media.musicasacra.com/pdf/whychant.pdf

This is quite good

Here is the PDF youtube chant and polyphony comments file for anybody interested.