When you break it down, there are four tricks that an artist uses to make a critter cute.
- They'll give it a large head, eyes, and possibly feet. Stubby limbs in comparison to the body are also sometimes present. Since those are common features of young animals, and since humans instinctively want to nurture and protect babies of all types, this resonates on an instinct level with the audience.
- They'll make it soft and huggable looking, by having no hard angles and/or being covered in plush fur. This has the added benefit of making it easier to make into merchandise, as well.
- They'll give it a low volume but high pitched cry. Like 1, this makes the animal seem more like an infant, and thus brings out our protective instincts. The best range is the range infant humans make noises in. This is incidentally the same range that kittens and some adult cats make noises in, which may be one of the reasons humans find kittens so gosh-darned adorable.
- They'll be small enough to be easily picked up and cuddled. Once that critter has brought all those protective and nurturing instincts to the fore, feeling like you could actually scoop the cute widdle guy up and snuggle with him is the icing on the proverbial cake.