I would have them walk slowly down the tracks rather than just stand there - these are beautiful shots, but it kind of looks like they are just standing there waiting for a train to come. Walking down the tracks (at least in the first photo where they are facing away from the camera) would make the photo more interesting, like a sense of adventure or journey. With the first photo, I would also adjust the colors so that the sky was still as it appeared in person - it has beautiful, soft colors that would increase the warmth of the photo.
The the lighting and colors in the second photo is great, my only beef with it is that the family posing looks very symmetrical and a bit unnatural. It would create an interesting effect if the subjects were posing differently from one another, maybe one or two of them sitting or crouching, holding hands but without looking "forced". The third photo also displays excellent lighting (I know I wouldn't be able to capture an image like that in the dimming light), the only thing I can think of would be having the boy sitting on the other side of the track and then getting more of the background in the photo (the train tracks going off into the sunset).
Hope this helps, and great photos.