Wonderful photograph.
You’ve done so many technical and artistic things right with this photograph. As you’ve mentioned, you’ve done a great job of isolating your main object from your background by using a shallow depth of field. Otherwise, the colors would have blended and your main object would not have been pronounced. The image would have also lacked focus and secondary, unnecessary background object would have made it into the photograph.
The color control in the photograph is great. The earth tones contrasted with the highly saturated blues and pink gives the photograph a unique color appeal.
Make sure you’re careful with subtle amputation. Notice how the child’s fingers are cut off by the right wall of the photograph. This looks accidental and could have been fixed by simply changing your position a few inches. Other than that, the composition is great.
Next time you’re on a beach I think you’d benefit from playing with the textures that exist there. For example, sand presents the opportunity to play with one of the most interesting and readily available textures. Look at the following photographs for example:
http://www.toxel.com/wp-content/uploads/2008/11/musesandphoto15.jpg
http://www.alonsodr.com/gallery/d/1050-2/sand_sailing.jpg
http://farm1.static.flickr.com/86/234705029_9006e65305.jpg
http://images-2.redbubble.net/img/art/size:large/view:main/823079-2-face-in-the-sand.jpg
Great work!