The theme of a book is an ‘abstract idea’ such as friendship, loyalty or a quest for identity. It is important to understand what the theme of your book is. Often the theme does not become apparent until you have finished writing the book. Themes in children’s picture books can often be identified by three categories: daily life, family and feelings. The Baby who wouldn’t go to bed by Helen Cooper has a theme of bedtime routines, which are part of daily life.

Themes are different to morals. A good rule of thumb is to avoid preaching. Children’s stories should be explorations of life—not Sunday school lessons. The theme should be subtle and will strengthen the story, as it adds depth and meaning.

Behind a very simple structure, brief text and beautiful illustrations lay truths that are timeless. The story should leave readers with a residual feeling. There has to be something deeply felt that stays with the reader afterwards. You should be able to sum up your theme in one or two words. The theme of Not now Bernard by David McKee is busy parents, which is something all children can identify with.

Your characters will always carry the theme but don’t confuse theme with the story’s plot. The plot is  what happens in the story and the order of the story’s events. A theme is an insight or viewpoint or concept that a story conveys. If an editor says your story is ‘slight,’ this may mean you have no significant theme.The theme of Where the Wild things are by Maurice Sendak is dealing with the feeling of anger. 

Maurice Sendak does not to blurt out his theme. He lets it emerge from the story. If you must come out and say it, do it in dialogue, not narration. Keep the theme positive. If writing about a social problem, offer constructive ways for your readers to deal with it.