Actually, all of the boys (with the exception of Simon, the Christ figure) have lost their innocence, even Piggy. After all, Piggy joined in the dance one stormy night and helped kill Simon with all the rest; Simon, who was merely bringing the boys the news that the beast was only a dead pilot.
Tracking the boys' degeneration through the novel, one can see them, little by little, slowly shedding their innocence along with their clothing, until finally, they become much like an ancient civilization that practices human sacrifice to their gods to keep them at bay (thus the plans for Ralph's head on a stick as a present for "the beast").
And the final irony? To be rescued from their little war by adults who appear on a battleship, armed to the hilt for their own war--men who have lost their own innocence and have darkness in their own hearts. There is nobody who can truly save them, then.