Poor light quality and direction, exposure issues, white balance issues. Note the color of the young girls scelera (eye whites). They are not white. It looks like something is reflecting a greenish color cast on her face. I did an edit and while the upper part of her forehead and arms look ok her facial mask is still an odd color. See my edit below. Learn Photography Concepts
I'm just going to go over some of the post processing since no mater the composition the processing is what hurts the photos for me.
Photo number 1 and 4. Black and white normally have every shade from white to black. Neither of these examples have white which makes them look flat.
Photo 2. Dial way back on the saturation. That flower drags the eye away from the subject and looks like you were trying to go for HDR portrait which is never good.
Photo 3. Possibly brightened just a bit to much and surely to much saturation but not as bad as # 2. Dial back the saturation and possibly drop the exposure by 1/3 stop.