Perhaps the child represents the captain when he was younger. In his quest to return to his carefree, simpler youth, the captain has to be granted it's permission before he can go back. However, his youth doesn't want let him in because the captain's been stained by all the wrong deeds he's done. The final stanza is the captain trying to apologize to his youth about the terrible things he's done.
An addeneum to my previous post:
Perhaps the child represents the captain when he was younger. In his quest to return to his carefree, simpler youth, the captain has to be granted it's permission before he can go back. However, his youth doesn't want let him in because the captain's been stained by all the wrong deeds he's done. The final stanza is the captain trying to apologize to his youth about the terrible things he's done.