Supporting characters help to convey the context of the story. In deciding who else to add to your children's book's cast of characters, ask yourself who you need in addition to your main character to tell your story. “Who does my main character need around her to make her believable as well as to help her carry out her destiny?”
For example, in 99 percent of stories, the main character needs at least one other character to speak to and interact with (and have conflict with) no matter what your story is or how long it is.
Enter supporting characters. For example, if your story takes place 150 years ago, supporting characters could show how life was back then: blacksmiths, butchers, street cops on horseback, one-room schoolhouses filled with children of all ages, and the like.
Additionally, supporting characters can be
Catalysts in the plot, causing events to occur or information to be shared: If your story is about a boy who is looking for some hidden information, perhaps your supporting character tells him a story about her grandmother, showing Barnaby a photo album that gives him a clue as to its whereabouts. Or maybe your supporting character unwittingly leads the enemy right to your main character’s secret hideout.
So dissimilar to the main character so as to highlight the main character’s assets or flaws: Perhaps your main character is an introvert. His best friend, your supporting character, is an extrovert. The outgoing one puts your main character in a situation causing him extreme discomfort, which in turn leads him to do something completely out of character or perhaps something to totally mess up his life.
Unlike main characters who have to push the story and plot further, supporting characters don’t have that limitation and thus can often be colorful, silly, super-brave, or even magical. Literally, they support the main character’s journey, whatever that is. Think Tinkerbell in Peter Pan and Donkey in the movie Shrek. Whomever you choose for your supporting cast, make them three-dimensional and avoid stereotypes.
You develop supporting characters as you need them in your story, and that becomes apparent as your plot calls for someone for the main character to interact with at various points in your plot to pull the story forward. You can ask many of the same questions about the supporting characters as you do about the main character in order to develop them, but you needn’t go into quite as much detail.
Here are some steps to help you develop supporting characters:
Decide the function of the supporting character in your story.
For example, is the primary reason for including this character so that you have someone who can serve as a foil between your main character and his goal? Or is the supporting character one whose job it is to serve as the conscience of the group, reminding them of the correct path to take, while they insist on going the other way?
Figure out what the function of the supporting character is in relation to your main character.
In other words, how does this supporting character support the development of the main character? Children might need parents or adults around them to highlight their uniquely childlike perspectives.
Flesh out the supporting character by adding in details.
Create a character bible just as you would for your main character.
After you create the supporting character, figure out how her differences from the other characters help her fulfill her function regarding the plot.
Step into the supporting character’s shoes.
When you’re writing this supporting character, imagine yourself inside that person’s head: What is she thinking right now? What is she seeing? What impulses or emotions is she showing or suppressing? What does she notice while another person is talking? What is her mood? All these markers will help you make her real — which is important, no matter how minor a character she is.
No matter how minor a role, if a supporting character is worth mentioning by name, she is critical enough to warrant your attention. She will have a point of view, an attitude, particular behaviors, a personality — even if you only glimpse a bit of these attributes.
Whether she is there to help convey the theme of your story or move the action forward at a crucial point, she is there to add to your story’s flesh and bones.