I’ve always thought that Derpy being Dinky’s mother was a terrible and sad fan theory (e.g. because of “a single mother left by some colt” version of it). Not to mention that random background events and character placement pretty much contradict this.
Now that’s my headcanon - Dinky is a filly obssessed with Derpy, due to their color similarity, but Derpy is not her mother (and has never been ofc). Makes as much sense as them being a family (btw, I saw some people actually take random things from the show and take it as ‘proofs’ of them being an intended in-universe family, heh).

In the background we can see 4 OC’s.
megaphonnic’s Face Ache is selling bubble gum, Sketchywolf-13’s Sketchy is selling toys - this is a resocialization program they were forced into during their multiple life sentences served in Canterlot prison - they are magically bound to those stands and are supposed to do an honest work selling appropriate stuff. Any attempts to leave the stand will knock them out. And there is a Royal Guard off-screen. You can see how happy they are with their new roles
Then we can see an OC of my Patreon supporter - koobikitsune’s Rhythm a capella (Standing next to Zecora’s stand) and Szafalesiaka’s (my RL friend) ponysona who’s been cut in half by the edge of the picture.

Thanks to Midnight–Blaze for his advice :>