Mr. Cat's human form wears a loose-fitting jacket and oversized pants. It's not too hard to imagine why a young boy with body image issues would wear clothing that conceals most of his figure.
Stumpy takes the bottom bunk on the bed in the prison cell because he's afraid of heights.
Kaeloo's human form is clearly a girl. Her frog form looks androgynous because she's a frog and frogs can be hermaphrodites, whereas humans are typically one sex or the other, excluding intersex individuals.
