The hottest market in children’s writing currently is juvenile fiction for eight to twelve year-olds. These fourth through sixth grade books have the larger type. They normally contain about 20,000 words, and they don’t have pictures.
These are fast-moving books with lots of exciting action. The dialogue must be believable and true to that age group. Normally they are geared to either girls or boys. They contain strong character development. These plots are more complex involving sub-plots and secondary characters that are woven through the story. Kids get hooked on characters at this age, which explains the popularity of a series. Thus, a publishing house will want a series of these, so you need to think in multiple books if you want to write these. Occasionally, you might be able to fit your book into an already existing series.
All the qualities that make good adult fiction make good juvenile fiction: conflict, suspense, pacing, focused plotting, complex characters, a strong beginning, a tense middle, and a satisfying ending.