drdiesel1 gave you some great feedback, and I agree with it completely, so won't reiterate. The third shot is a great example of why you need to manage the clothing of your subject to get the best image possible. You need to try your best to get your subjects to wear LONG sleeves, for a variety of reasons.
The main reason is that when skin is showing like the girl's arm in shot 3, you have two areas of light, white skin that are competing for attention. You do NOT want that. You want the viewer's eyes to go to the face and not be drawn away by the second competing white element, the arm skin. The pretty lady in the second shot, got it right. Notice how your eyes stay on her and the baby? This "rule" (which was meant to be broken situationally) is the same for women or men wearing shorts. Just say no.
The second reason, especially for women, is that the skin tones in bare arm skin and a face with make up (or a sun tan for men) is completely different. Look at her arms and compare it to her face. night and day. Long sleeves would change everything in that regard.
A third reason to urge women to wear long sleeves is that 95% of women, fat or thin, hate their arms in photos. Good posing techniques can slim arms down, so can photoshop and lighting, but many women will whine about their arms in photos and they should have worn long sleeves anyway, for other reasons also.
Keep shooting, you are off to terrific start.