The words "niece" and "nephew" categorize by gender, but that's not something we want to do by default in the more beautiful world that we are building.
In the world we're building, you usually treat your niblings the same, regardless of their gender identity. In the world we're building, families don't impose an unnecessary gender identity on children which makes it harder for children to discover their gender on their own.
The term "nibling" is just as useful as "sibling," but way, way, cuter. Niblings! Adorable! Plus it only contains 40% of the syllables of "nieces and nephews," so it just rolls off the tongue, making you a model of linguistic efficiency. Call them your niblings. They'll thank you later.
Thank you for the original photography: Suzy Hazelwood, Sharon McCutcheon, and, most of all, Bink.