Is khuôn the classifier for face?
"Khuôn" can be "Shape" or "Mold". "Bụ bẫm" is an adj used to describe a face or body, arms and legs. "Khuôn mặt" means the shape of its face.
Bụ bẫm usually use to describe a baby, not a cat.
True, a Vietnamese friend just told me that the word is mostly used to describe babies.