Lots of times my students confuse fiction and nonfiction. I remember having my own problems with this as a child. We tell them, "fiction means Not real" and "nonfiction means real." Many students say they get them confused because of that silly little "N."
Try this: "Fiction means Fake" and "NonFiction means Not Fake." Now the N's AND the F's line up.
I've received positive responses from kids when they are first learning the two genres, and they often say, "I get it now." They also tend to learn the 2 types faster. Once they are confident in and understand the two types, and they begin to learn the genres within the categories, we redefine them to the "real" and "not real."