It can often take a good long time on location between setting up the camera in a position and getting a final shot. There's lighting, staging, cleanup, and...often more lighting to do before everything's solid and we move on to the next image. Particularly in a family home, people can unwittingly (or sometimes intentionally) walk through the scene during that time. And in rare instances, what they leave behind is even...a-track-tive. Yep, couldn't resist.
I considered leaving the footprints in this image for the final version, but decided against it. Next time I shoot a kid's room, though...