What do the boys look like as they hike along the shore?

As Roger and Jack approach the shore the other boys are described as "inkstains."

As they came to the last slope, Jack and Roger drew near, changed from the ink-stains to distinguishable figures. By common consent they stopped and crouched together. Behind them, on the horizon, was a patch of lighter sky where in a moment the moon would rise. The wind roared once in the forest and pushed their rags against them."