This photography tip is a long time in coming as it is one of the things that bothers me the most, that being having the horizon cut right through the subject's head in portrait photography. Living in Florida there is never a beach very far away, meaning there is a distinct horizon in the background of photographs. When composing a portrait, I always make sure the subject's head is above the horizon for a single subject. Sometimes in group shots with very tall people and kids mixed, it is not always entirely possible, but for sure I will have the adult's heads above the horizon.
So when you are out shooting on the beach next time, or anywhere that the horizon can clearly be seen, be sure to get the subject's head above the horizon. The horizon going through the head of the subject is very distracting. Just get lower when shooting to avoid this. When photographing children, like in the example above, you may have to get quite low, often going on to one knee. It is worth it though!