I took an online photography workshop a few months ago and the instructor emphasized the connection between the subject and the photographer. Now, that's not to say all photos have to include someone looking into the camera, but it did highlight a difference between photos that are simply fine and ones that are filled with (or elicit) emotion. In this case, I think her joy is pretty evident, which is why it's one of my favorites.
@vera365 Vera, I enjoyed it a lot, although I have to admit that I haven't taken many classes--just some basics. This was the first one I took from Clickin' Moms and it's called The Messy View by Tarah Sweeney. She's a local (Southern California) photographer and a mom of small children, so a lot of her examples were very relatable to me (beach settings, kids playing, etc.). I think it was well worth the $60 I paid.