@EPPony
 
That’s fine, but we really need to have a solution for an official tag here (unless the artist who drew a picture made up a relationship between them for his picture), until the show or comics provide us with more infos about them.  
And deciding for a good tag can really only work if we go with what the show already gave us, and think this over logically.
 
The fact that Crackle Pop was never seen in Ponyville before, in five and a half seasons, while Dinky and Derpy were seen plenty, sometimes even together by now, is pointing very strongly into the direction that Crackle Pop isn’t living in Ponyville, even though he would have no reason to not live there as Derpy’s son and Dinky’s brother.  
So, he’s most likely coming from somewhere else, which makes it very unlikely that he is Derpy’s son, and much more likely he is her little brother, who still lives with their parents in that other place.  
Doesn’t keep anyone from thinking what he wants, but we need to settle for an official tag until a possible reveal one day and uncle and niece is really the most likely relationship for Dinky and Crackle, so far, by what we have seen in the show up to this point.  
That’s why I keep pushing for that tag.

@Wiimeiser  
Personally, I see them as brother and sister, with Dinky being the older of the two, like Chirpy is with Dipsy.

@Wiimeiser
 
Yep. With Crackle Pop never having been seen in Ponyville before (which is another indicator for him not being Derpy’s son), it’s pretty much guaranteed that he came over from Rainbow Falls to participate with his big sister in the Applewood Derby. Which makes him and Chirpy Hooves twin siblings, which is exactly what I think they are.  
Coincidentally, there is a fic for that too:
 
http://www.fimfiction.net/story/342777/fate-must-be-cruel-only-to-the-kind
 
 
Except that they aren’t twin siblings in this fic. It worked better for that fic to have them as big brother and little sister, so I went with this instead.

Wait, uncle and niece? I thought they were fraternal twins…

@DankHooves
 
Me too! :D

In my own Crackle Pop isn’t a good name for him and the Hooves family. Sorry.

Its nice to see Derpy’s family grow larger :D

He never speaks, so his name doesn’t appear in the credits. I think it’s safe to name him Crackle Pop.
 
I now imagine a scene in which he goes absolutely insane. Call it “Snap, Crackle Pop”.

Eh, guess Crackle Pop wouldn’t be too bad of name for him.