"Faction," as in a combination of fiction and facts, is not a good option. First of all, lots of fiction books incorporate terrific backstory...factual details and people, places, and things. Many fiction writers do tremendous research for their settings. So if you go down the road of "faction" then you'll have to start thinking about percentages of fact and fiction!
When I talk about nonfiction with kids and adults, I use not only the term nonfiction, but also its subcategories: expository nonfiction and narrative nonfiction. I write both these kinds of books. My book, Stars Beneath Your Bed: the Surprising Story of Dust would qualify as expository nonfiction. It explains what dust is made of and how it influences the colors of the sunrise and sunsets. Trout Are Made of Trees does the same. Either of these books, if you wrote out the text without pictures, would seem like an essay, an explanation, an exploration of a concept.
Many of my other books, such as Vulture View, Dig, Wait, Listen: a Desert Toads Tale, and The Bumblebee Queen , are narrative nonfiction. Another good example is the book Arrowhawk by Lola Schaefer. These books use narrative techniques to bring nonfiction to life. Suspense, pacing, plot, character...all these are narrative techniques. They are not unique to fiction People use these very same techniques to make their own "true" life stories dramatic. What I like about the term "narrative" is that it does not assume that these techniques belong to fiction and are somehow being co-opted by nonfiction writers. No...they are the elements of stories, both true and false.