When we have multiple ships built along similar designs, it's customary to refer to them by the initial example of the design. For example, the last American battleships are called Iowa-class, after their lead ship the Iowa. Until recently, Nora (22mo) used this in naming people. This included, at various times:

• "Mama"-class: parents. Julia, me.
• "Anna"-class: siblings, or maybe children. Most commonly Anna and Lily.
• "Weiwei"-class: housemates. Most commonly Weiwei and Andrew.
• [Not Nora but Lily] "Ella"-class: cats. Most commonly our cat at the time, Ella.

Lily really didn't like being called "Anna". Possibly Lily would have minded less if I'd been able to teach Nora to say "Anna-class", but I doubt it: the real hurt was not being the class exemplar. Nora also had a period when she would correct us: whenever anyone said "Lily" she would firmly say "Anna!"

This system makes a lot of sense when you consider how few words she had to work with. Much better to allocate just one of your ~10 words to siblings, and you don't hear the word general word (ex: "sibling") enough for that to be the word you use.

(The post's title would be confusing, except that we've had Classless Inter-Domain Routing for thirty years now.)