I do as well.

As for me, I see them as mother/son since you don't really see many mother/son duos in the show or the fandom, especially when you exclude the mane 6 and OCs, plus, I could see Derpy having sent Crackle to live with her siblings due to being unable to take care of both of them and going off to visit him at times, leaving Dinky to be looked after by Amethyst and Carrot Top.