Final answer:
The correct revision is B, changing 'theirselves' to 'themselves' to correct the reflexive pronoun use in the sentence.
Step-by-step explanation:
The revision that should be made is: B. change theirselves to themselves. This is because theirselves is not a word in the English language. The correct reflexive form of they when used as a subject is themselves. The sentence should read, "After all the toys were loaded into the sleigh, all the elves made themselves a big glass of chocolate milk."