These are ridiculously cute. If I had to suggest anything, I say maybe add a bit of highlight to the hair. The only biggie is that at chibi size, I really wouldn't be able to tell at a glance the difference between the male and female sprites with the brown hair. In fact, even looking closely, I'd be hard pressed to differentiate gender. I think a bit more differentiation would be helpful. Maybe keep the biggish legs on the male and shrink the feet of the female and bring them closer together (to give her more "womanly" hips).