How does Jerry's journey end, and what does the bay mean to him at the end of the story?

Jerry's journey ends almost where it began: warm and safe with his mother, but with a new sense that he is happy to be there.  Initially, he was eager to go to the "wild bay" rather than to their usual "safe beach" with her, the wild bay symbolizing maturity and the safe beach symbolizing childhood.  He longed for independence, and his mother struggled with just how much freedom to give him.  

After his trials in preparing to swim through the underwater tunnel in the "wild bay," and the trauma of actually doing it, Jerry seems to find that he is not quite ready to be the adult he wanted to be at the beginning of the story.  Though, at first, he yearned to swim with "the big boys [who seemed like] men to [him]," by the end, "He did not want them."  What he does want is his mother's praise and approbation.  "'Mummy,' he said, 'I can stay under water for two minutes -- three minutes at least.'  It came bursting out of him."  Just like a child who blurts out news, especially claims about the amazing things he can do, Jerry seems quite childlike in the end, fishing for her praise and admiration.

After he swam through the tunnel, he'd come home pale, bloody, and tear-stained. Even after cleaning himself up, his mother could tell that he'd been injured.  When she insisted that he stay home for the remainder of the day, "he gave in at once.  It was no longer of the least importance to go to the bay."  In other words, he no longer desires to grow up so quickly.  The wild bay was characterized by water stained with "purple and darker blue," like a bruise, and rocks like "discoloured monsters under the surface."  There were cold currents to shock him, "fanged and angry boulders," and "salt that was so painful in his eyes that he could not see."  Like adulthood, the wild bay is unpredictable and dangerous.  At first, Jerry was exhilarated by his freedom there, but but he later realizes that "He wanted nothing but to get back home and lie down."  Rather than a place to escape, home (and the safety of childhood) seems pretty desirable to him now.  He knows he doesn't have the maturity to swim in the wild bay yet.