Well what exactly do you want the genre to be? Non fiction, fiction, sci-fi, fantasy, etc. I would suggest you do fiction or fantasy because I think they're the most easiest genre's to do, plus you can use your imagination to any extent.
If you're doing fantasy you can write about any creature, like a fairy, unicorn, etc. It could be about them discovering a new place or something else.
If you're writing fiction, it could be about a group of kids who deal with the troubles of ordinary life, or something similar.