The first-ever picture book from Adam Kay and Henry Paker.
 
This is the hilarious (and admittedly a tiny bit gross) tale of Amy, a small piece of sweetcorn who is eaten by Noah, a medium-sized boy. The story follows Amy on her funny, gooey and anatomically-accurate adventure through the human body as she discovers lots of facts about digestion. (It's fair to say that parents might learn a little bit too.)
 
Age 4+