When they came back they found out that Rita was murdered by the Trinity Killer and went into shock. For a brief time the children lived with Dexter until Astor wanted to move in with him and his wife. They eventually became Astor and Cody's legal guardians while Dexter keeps Harrison.
They eventually come down to Miami for Harrison's birthday to the surprise of Dexter. They then reveal that Astor and Cody want to spend the summer with Dexter.