Answer:
The author of On Turning Ten includes fantasy elements to make the reader remember and envision how magical being a child is. When you're a child, everything is fairytale and you trully believe that you can "become invisible by drinking a glass of milk a certain way" or that somehow, in some story, you're a prince. It's the magic and fantasy of being a kid, that, for the author, it starts to fade little by little, and the turnpoint of entering "real life" is when you became ten years old.
