In what senses is the island a haven for the boys? In what senses is the boys situation frightening?

The island is a haven because for the first time in their lives, the boys are free of authority. They can swim, play in the sand, run in the forest, explore, and have fun. It isn't a haven because the boys are suddenly responsible for providing their own shelter, finding their own food, taking care of each other. There are also those mysterious things that make noise in the night.