I insisted that all my nephews and nieces called me by my first name.
When you're a kid you add the Auntie/Uncle, when you get older you move onto first names. Simple.
just to put it out there, its more a respect thing, why not call your mom/dad by their names either?
in asian culture, we "think" its respectful to not call people (Older than us) by their name and instead say uncle, auntie etc etc
When you're a kid you add the Auntie/Uncle, when you get older you move onto first names. Simple.