A trans parent would likely still want to be called “Mom” or “Dad”, I assume. At least that’s the case with the few trans parents I know.
Parents don’t usually use “daughter” or “son” as pronouns, so I don’t think it would come up with non-binary children.
Do children of non-binary parents call their parents by their first name? It seems unlikely that they say “Parent, may I please have more screen time?”.
Very individualized as per need. Non-binary is an umbrella term for a whole bunch of different situations so what feels right is going to be very different for someone who feels like say a mix of masculine and feminine versus someone who has dysphoric reactions to any and all gender markers. It’s going to be different for someone whose identity is more static than say someone who fluidly bounces between extremes.
If you know someone who is non-binary that’s essentially just the tip of the iceberg of a whole discussion about how they personally interact with their body or the culture of gender. A lot of people seem to treat it as a full stop third category which can actually be a disservice to a non-binary person because it oftentimes just leads to a lot of new assumptions and frames out some of the ways they could be better treated than just as automatically genderless. I’ve heard of mixes of Mom/Dad for bigender people, just Mom or Dad for trans masc/femme folk, Completely new words that do not have cultural baggage, or just “my parent”. It’s not a one size fits all situation.
I appreciate the thoughtful reply.