This photo exemplifies short depth of field. With that, it also uses contrast in order to create an image where the young boy in the foreground, stands out from the background. This contributes to the depth of field in this image, with the young boy in focus and the background out of focus. The light background allows the boy to stand out, making this image very powerful.
This photo exemplifies a long depth of field. With the entire image in focus, it allows the viewer to get a greater understanding of the moment. Having a long depth of field in this image is important to its composition because otherwise you could not see the happy expression on the subject face.