I could say this with a single sentence but I plan to go on a tangent. Young Adult and Middle Grade are not genres of children’s literature.
But they have their own sections at the bookstore.
No kidding. Kids have their own sections at the department store too, but it’s not meant to do anything other than dictate what sizes the pants are.
Young Adult and Middle Grade are age categories of literature, meant to describe the ages of the intended audience.
A genre would be fantasy, science fiction, paranormal, suspense, romance, dystopian, etc.
It’s important that you understand the age category that you are writing in. Unicorns do not make a middle grade story any more than romance makes a YA. Each age category has content restrictions and expectations on voice. And to make matters more complicated, they both have upper and lower distinctions where they cross over with other age categories.
Lower middle grade is between 8 and 10 years, upper middle grade is between 10 and 13.
A middle grade novel can be anywhere from 35,000-80,000 words depending on the genre. Lower middle grade and contemporary will be at the lower end of this word coutn spectrum, while upper middle grade and science fiction/fantasy work will be closer to 80,000.
Some middle grade readers are as old as 14. There currently is no name for the gap between middle grade and young adult, so you need to remember that kids read up. You may target your book for 12 year olds but a bulk of your audience will be voracious 8 year old readers.
Lower young adult is between 13 and 15, while upper young adult is between 14 and 18.
Just like middle grade, young adult has overlap with itself. And, just like with middle grade, kids read up. There are some middle school students reading upper young adult novels because they are advanced readers.
Writing is these age categories requires an understanding of voice, regardless of the genre that you are writing in.
Writing in the appropriate voice is probably the hardest thing about writing children’s lit. You don’t just have to just worry about the words on the page and the age appropriate way to say them, but also how it sounds.
Genre describes your work in terms of setting, content, and style. The three major genres of setting are fiction, fantasy, and science fiction. Fiction refers to a realistic setting. Science fiction and fantasy refer to made up settings.
There are too many subgenres to list in this discussion but they include adventure, romance, dystopian, space opera (which can be fantasy too, see Star Wars), mystery, thriller, horror, historical, western, and many others.
As you may remember from your English classes, there are many styles of writing like short story, novella, novel, poetry and verse, multimedia. Some styles are about length, such as the short story and the novella, while others are about form, such as poetry and multimedia work.
It’s the combination of these genres and subgenres that make each piece unique, but it is the mixture of voice, the age of the protagonist, and the content of the story which determine its age category. So, while fantasy is apopular genre, you can absolutely write that historical science fiction novel featuring a twelve year old protagonist who builds robots to save the world.