These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: At least in the early episodes, when someone mentions a number higher than 7, the monsters broke into a song and dance, ending with asking the person to never mention the number. It never got a reaction and was ignored immediately afterwards.
Fridge Horror: How did the monsters' tiny mother conceive or give birth to seven giant monsters? Septuplets at that.
More to the point, who was 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.
Fridge Logic: If their mom is a human, wouldn't that technically make them only half-monsters?