This new series of books about bodies for kids covers several different aspects of what is going on with you and why.
My Itchy Body
My Healthy Body
My Stretchy Body
My Noisy Body
My Messy Body
My Achy Body
by Liza Frommer & Francine Gerstein
Tundra Books
This series of books covers various body-related topics, each in its own title. My Healthy Body covers, essentially, maintenance and hygiene, talking about the importance of nutrition, exercise, sleep, eye and dental care, and more. My Itchy Body talks about various kinds of irritations that lead to itching, and how they affect your skin, while My Achy Body is about the various reason and ways that bodies can hurt and become sore. One point – muscles, anyone? Next title – My Stretchy Body! Heh. The Noisy and Messy books cover the stuff that delights kids – the gross stuff, and weird body noises, as the titles suggest.
These do not discuss how the body systems work, or go into diseases, and they are lighter and more conversational in tone than what you would want for researching a project, but they are a fun look at the body for a kid who is fascinated, though you might later need to add a heftier title that includes all that other info.