One Last Sandcastle!

"One last sandcastle! One last sandcastle!" he shouted, before turning his back to us and running to the beach, the back of his head defined by the setting sun as he ran. This is all I can see at night. The image of him running to go knock down another sandcastle burnt into my memories.
But then what? What happened on that beach? If only i knew what happened to him after, then maybe I could see him again, or at the least, sleep again.