How did the monsters' tiny mother conceive or give birth to seven giant monsters? Septuplets at that.
Maybe they started out like regular sized babies or their mom is a shapeshifting humanoid monster and could change her size based to accommodate her pregnancy and conception.
The episode where they eventually wind up aging backwards does show that they were smaller at one point, however it is also magic that's doing it, so one might need to take that with a grain of salt.
More to the point, who and where is their dad??
They're probably adopted.
There's also a theory that their mom is a monster in disguise, or maybe a witch, and created them with magic.
That would be unlikely as their mom said one of the kids looked like his dad.
A lot of the materials say she's a witch, though, she ain't in the book. As far as the shapeshiftin' goes, well, she's not shown with the same consistent hair color, as, in scenes it's gray, some have it blonde, and others peg her as a brunette (black or brown hair). As far as the monsters being smaller as babies, well, they kids in monster years and so prolly spends a long time as babies.
If their mom is a human, wouldn't that technically make them only half-monsters?
Well, a couple of them do look a little human-ish.
As far as we know, the series never fully confirms Mom is the monsters’ biological mother. The closest it comes is when she tells Two he looks a lot like his father. This can be implied to mean the pair were intimate, but it doesn’t have to mean she is their biological mother.
