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The ground beneath them was a bank covered with sparse grass, torn everywhere by the upheavals of fallen trees, scattered with decaying coconuts and palm saplings. Behind this was the darkness of the forest proper and the open space of the scar. (1.52)
The boys may not be afraid yet, but we're getting a bad feeling. This passage, with its "decaying coconuts" and forest "darkness" hints that nasty things are on the way. No wonder the littluns start freaking out.
“We may stay here till we die.”
With that word the heat began to increase till it became a threatening weight and the lagoon attacked them with a blinding effulgence. (1.125)
When Piggy says the word "die," he seems to bring fear into the island. He and Ralph don't even know that anyone else is on the island yet—but it probably would have been better for them if they'd been alone.
Within the diamond haze of the beach something dark was fumbling along. Ralph saw it first, and watched until the intentness of his gaze drew all eyes that way. Then the creature stepped from mirage onto clear sand, and they saw that the darkness was not all shadow but mostly clothing. The creature was a party of boys […]. (1.184)
Ralph doesn't exactly seem afraid here, but maybe he should be: the boys choir appears out of the "mirage" as a man-beast. (Don't worry; he'll be afraid later.)