Image doesn't meet our quality standards - Critique please!

Don't change to monochrome.

Your first needs noise reduction. You need to check the boots for logos.  I'm not sure, however: I think that some errors have been introduced with your fancy filter that you applied. I suppose you have submitted a model release signed by the father and the mother (one as witness).

Your second requires probably some exposure work to be done: lifting the shadows mainly. If you can secure a model release from the lady, that would be ideal.

You should send in copy here the original pictures as we can't really check all the errors on downsampled assets, but I believe that you only changed 300 ppi to 72 ppi, so that should do it.

(edited)

No, you shouldn't downsize images prior to uploading them here; nevertheless the technical issue is immediately apparent. Adobe doesn't accept images that have been converted to black and white, or, in this case, sepia. The first image, which is lovely by the way, also has a blown hotspot in the horse's face. The second image has underexposed shadows.