You're teaching how to write a memoir in the Writer's Workshop...you need a mentor text.
If you've never used Memoirs of a Goldfish, by Devin Scillian, now's the time to check this book out! What can I say? It's precious!
Told from a goldfish's point-of-view, Memoirs of a Goldfish is a sweet romp through the aquarium, complete with the addition of new fish, a bottom feeder, and a disturbing new friend that may or may not be a part of the scenery.
There's a great little bonus to this book...an interactive app with the same name is available for purchase on iTunes. It's a pricey little app ($4.99), but it allows you to extend the experience for your writers.
Memoirs of a Goldfish is a book that would work equally well as a mentor text in a first grade and a fourth grade classroom. It has appeal that spans many grade levels.
Other books that follow a similar vein would be Diary of a Worm, Diary of a Spider, and Diary of a Fly by Doreen Cronin.
If you haven't tried using these mentor texts with your students, I'd highly encourage it as they are very engaging!
Have fun and write on!