What I'm about to say may sound weird, but it may work.
The first step is to outline an immature character in a childlike way (always happy, always interested in everything, always smiling, and joyful) and pretend that he or she is part of (Edit because I wrote it wrong:) a royal family. Now, put that character among chilvarous people (the reason for their behavior being that character's social status). Getting to the hard part: You know when you're writing a story with some details still unknown to the reader? Those kinds of information that only you know about, and that makes the character behave in a certain way? Good. Keep all of the above information for yourself so that your teacher wouldn't figure out what you really did (what the characters are like and the reasons behind their behavior).
Otherwise, I have no idea.
