When Lian Harper is three years old, she starts understanding that when her aunts and uncles are in uniform, they have different names. However, some names reflexively get shortened to make it easier for her to say.
"Nightwing" becomes "Uncle ‘Wing."
"Blue Beetle" becomes simply "Uncle Blue."
"Zatanna" becomes "Aunt Zanna."
About that time, Arsenal!Roy Harper finally repairs enough ties with his family and friends to spend time around his “niece.” She first gets introduced to his working codename while past and current members of Young Justice are having an anniversary party at the Watchtower.
"Uncle Roy!" Lian says with delight.
"No, no squeaker," her father corrects with a fond smile. "Uncle Roy’s in his work clothes. Gotta call him his work name."
Three year old Lian blinks up at her father curiously as Arsenal!Roy can’t help but soften his gaze at his sweet little niece.
"When the mask is on, you gotta call him Uncle Arsenal, OK?"
Lian turns her head to look at her uncle, tilting her head one way, then the other.
There’s dead silence in the Watchtower hall as various people are either biting their lips or covering their mouths with their hands in an effort to stifle various shades of laughter that are trying to erupt.
Arsenal!Roy looks at Lian and her confused little expression for a moment, then sighs as he lifts her up into his arms. “I guess that sounds about right,” he chuckles with a wry smirk.