Firstly here are the broad reading levels:
Usually for children up to the age of 8 years old and have limited text and lots of illustrations.
5-8 years olds
9-11 year olds
Teens 12-13 and older
Within these groups there are also more specific reading levels but a lot of publishing companies have their own variations on this. This is just a guide but it is important to know where your story fits so you can target your exact age group.
These are stories that are simply imagined. Fantasy, adventure, concept, science fiction and the list goes on.
These are stories written about actual true events and facts. They can be about a real time and place in history or present. These stories are written with a lot of accuracy and very specific illustrations.
If you are going to write nonfiction children's books you must do your research and make sure everything is accurately portrayed. This is a very specific way of writing one which many publishing companies have a shortage of. There is a great market for this type of material however you need to be able to prove the accuracy of your work.
These subjects can be useful when figuring out where you fit within the publishing industries. You can use these categories to not only target your marketing better but also get published in the first place. Many publishers will specialise in a specific subject/genre. A great resource I found was 2011 Children's Writer's And Illustrator's Market
Arts and crafts