Charley Bates serves the same role as the Dodger—comic relief—but in a slightly different way. The Dodger is funny because he’s so knowing, and knows too much for his age, so that the contrast creates comedy. Charley is... just his dumb sidekick. Oh yeah: and he's consistently referred to as "Master Bates." Hardy har har, Dickens.
Master Bates (tee hee!) thinks everything is hilarious, and that crime is just one long joke against the system. That is, until Sikes murders Nancy. You could say that Charley is the one character in the novel that undergoes a major change: after the murder, Charley decides that crime isn’t actually so funny after all, and goes straight. In the final chapter, Dickens tells us that Charley became a farm hand and is pretty happy with a country life.