Nice job! You're really playing with some fun shapes. I'd love to see the texturing you could add to your characters like in the head sketches you included.
Some of these are stronger than others. The simpler, bolder ones tend to work better—when you're contrasting a large shape with smaller shapes, as in the first male silhouette and a couple of the female ones. I would look at proportions—the heads generally are too large and the bodies too small, making them seem like they have more cartoon proportions.