Boys' Vampire Costumes
Dracula was once a child. He may not have been as bloodthirsty in his youth as in his later life, but he had to start somewhere!
Once he's chosen a costume that's just the right combination of handsome and menacing, have him practice vampire behavior. Maybe (just for Halloween) let him stay up later than usual and be nocturnal. He can practice swirling his cape as he disappears, or train a pet bat. Oh, and don't forget the fake blood! Or, if he wants to really drink "blood," give him a dark-red-colored beverage. He can be as charming or as bloodthirsty as he wants to be.
Finally, teach him some good vampire lines. One would be a paraphrase of a line spoken by Bela Lugosi as Dracula: "I don't drink...juice."