Juvenile fiction needs to be very well written to gain any traction with parents, teachers and children. Aspiring children's authors need to learn how to craft an engaging plot, use age-appropriate language, and develop a finely tuned sense of the target market of their book.
The art of creating an engaging plot is the single most important factor in children's fiction. It's no good coming up with a setting and characters that lack a cohesive plot. What's the point of getting to know characters and trawling through long descriptions of settings if there is no story set there? What's the point of reading a book if there is no plot?
Young readers tend to be interested in characters who are self-sufficient but flawed, try their best but sometimes fail, want to do the right thing but have to deal with other characters who don't. In western culture these resilient values are what most parents and teachers try to instil in their charges.
Perhaps you know the plot for your story already, or perhaps you've only come up with the characters and setting. In either case, your characters and setting need to be enmeshed in an exciting, page-turning, bomb-ticking plot if you want children to read your book. Watch some children's TV shows in your target market to get a pared-back version of the structure of a narrative. TV shows are costly to produce and they follow a reliable formula and structure that is guaranteed to hook viewers, not just because of interesting characters and settings.
Your characters' adventure should occur through the entirety of the story, not right at the end. It is a mistake to spend too many words on setting up the orientation and not enough on the meat of the story (the problem or complication). The structure of a good, engaging narrative can be broken into three main parts and this structure is taught to grade one students in Australian primary schools. It can be further explained by seven sub-categories.
There is an orientation at the beginning then a problem or complication, a series of events related to that, then a climax followed by a short resolution. The description of different characters and settings should occur as needed by the plot or else the reader will not find it interesting. If they don't know why they should be interested in particular places or characters (i.e. if the reader knows they are not relevant to the plot) they will not read your book. This is doubly important for juvenile fiction. Kids' attention will wander if there's not an engaging plot from very early in the writing.
In most good narratives there are seven stages of the plot. If your juvenile fiction chapter book is 15,000-20,000 words here's roughly how many words you should spend on each segment:
Orientation
Main character - 500-1,000 words
Status quo - 500-2,000 words
Motivation - 1,000-2,000 words
Problem or complication
Initiating incident - 1,000-3,000 words
Developments - 4,000-7,000 words
Crisis/climax - 2,000-3,000 words
Resolution
Resolution - 1,000 words
The simple act of writing out the structure of your narrative will help you to self-edit and refocus your attention on a winning formula. After all, if nobody reads your book why publish it in the first place?