Sokka was captured by Fire Nation soldiers when they invaded his village. He got away from the soldiers, but only after they had left his village. He had no way to return to his home, so he's been living in the Fire Nation ever since. Zuko is kept hidden from the nation, apart from a select few. His father is ashamed of him because he isn't a bender. He isn't allowed outside palace walls and is a prisoner in his own home. - This story has been discontinued, but there is a summary of what was supposed to happen at the end if you'd still like to read :)