Why the images did not pass validation

I brightened up the eyes of the boy and you can see that his pupils, particularly the one on the right side, are not centered. I would steal one of the girl's irises (after some sharpening) and paste them over the boy's eyes.

I assume that the refusal was "quality issues". You did not mention that.

First:

The boy to the left is not sharp. With portraits the eyes need to be sharp. The girls face to the right contains artefacts, especially around her left eye. 

Your second: you may correct some of the snow flakes and you may correct the Hair, but there is nothing that disturbs me so much. 

All in all, and compared to other assets, the quality of these two pictures are excellent. It may well be that the moderator was rejecting by error here. 

First images: the boy's (girl's) scarf on the left. It looks kind of odd compared to the girl's scarf on the right. Remove the snowflakes from the girl's face and nose. Some "snowflakes" are out of focus, while others are overly sharp. Remove the out of focus ones, like the one above the subject on the left, above his/her eyebrow and on his shoulder. There are others. I'd use Gen Expand to finish out the tops of their stocking caps. Their eyes need brightening and maybe some catch lights to give them some sparkle. There's some black thing, maybe a collar, on the girl's coat on the right that could be removed. The teeth on both could be a little whiter. Just a tad.

Am I giving you the reasons why this image was rejected? No. I'm showing you what I would have corrected before I submitted these. Although that clump of a scarf around the boy's neck may be unfixable. It's even melded together at the bottom.

But all that said, you've got it going on when it comes to realistic skin, hair, and other facial features.