Introducing LinguisticsA Graphic Guide
This is an excellent book for young teens and up, providing a surprisingly dense overview of the history and theory of linguistics in a very easily digestible format. Especially recommended for anyone with ADHD: it has a comic book or scrapbook-like layout that keeps variety high. One of my earliest nonfiction book purchases, and a stellar example of how to explain a topic using a smooth progression of complexity.
Trask, R.L and Mayblin, Bill. Introducing Linguistics: A Graphic Guide. London: Totem Books, 2009. Printed Book8-184831-088-9.