"Pile up small mounds of sand together; build a fortress."
Far out on the background, you could see the state of the place before the children arrived. It is so barren and flat. It almost feels like the place gives a vibe of nothingness or blankness. But now that the children are here playing with the sand, they created these little mounds, changing the landscape of the place. Together, the place has evolved into a space rich in dimensions and full of memories.
Indeed, small changes made together create a huge impact, much like how little efforts of many people effect change, for better or for worse.