Background Pony Number 17 "[@Dust Rock":](/images/2495601#comment_9382072
)
I doubt Hasbro will ever confirm whether Luster Dawn is Sunburst's and Starlight Glimmer's kid.
They don't have to, actually--Luster Dawn was created for fanfic and fanart like this, so it's up to the fandom to give her a backstory.