Who is the boy talking with?

16.
M: I’ve got a headache.
W: Oh, don’t worry, little boy. Now open your mouth and say " Ah. "
   17.
W: Have you heard from your sister yet?
M: Yes, I got a letter from her yesterday. She said she enjoyed her visit to New York very much.
   18.
W: Is this your book, Steven?
M: No, it isn’t mine. It’s Sam’s.
   19.
W: Does your father smoke?
M: No, but he used to smoke.
   20.
M: Where does Miss King come from?
W: She comes from Tokyo.