Why not just call them a brood while your at it? It's because we're humans, and we don't like to be reminded that we're all just one worldwide catastrophe away from reverting back to savage animals.
Litter is usually reserved for animals that typically have more than one child at a time, it's normal for a dog, cat, mouse, etc. to have multiple babies at once, whereas with animals like humans, pandas, etc. it's a somewhat unusual occurrence so we call it something different
Twins and triples are words that contain information about the unusual number of children one had. Litter on the other hand is unspecific and is used to describe the group of newborn children of an animal for which it's typical to have more than one be born at the same time.
Now I just want some to come in to work and request a week off because their wife is about to have a litter of kids. Just think about the look on their bosses face
Until I had twins I didn't know they have a word for those of us born one at a time, singleton.
Now I catch myself using it in regular conversation and have to try not to. Example: "I've got twins and my bestie has twins and a singleton so we have to travel in her 7-seater van for day trips."
It only has a negative connotation because it is generally an "animal" word and humans believe themselves special and somehow above and separate from animals. It is the same with referring to someone using an object pronoun. Call someone "it" in English and see how fast they lose their shit. Like, mother fucker, you warp spacetime and have volume, you are a fucking object.
Unique perspective right there. I appreciate the rare respect for non human species though. Feels like the vast majority here has hierarchical thoughts when it comes to other species.
They're not clones though. For one, a clone has one parent and it's dna is identical to it's parent. Twins have two parents and their dna is only identical to each other.