Stories are usually narrated either in the first person (I, me, we, us) or the third person (he, she, it, they). Neither is right or wrong; they are just different.
Children love secrets, and a secret or a mystery can make a great plot, or add to one. Even if your main plot has nothing to do with a secret, it can add . . .
If we are going to write engaging and relevant Christian stories for children and teens, we need to be able to express deep emotions in the characters we create.