The Whipping Boy by Sid Fleishchman, 1987

Prince Horace aka Prince Brat is a naughty one - he can grease the saddles so that knights slip off their horses or dump bullfrogs in a moat so no one gets any sleep. He can even refuse to learn his reading, 'riting and 'rithmetic and no harm will come to him. And that's because he has his Whipping Boy Jemmy. A Whipping Boy, if you'd like to know, is someone else who gets the beating instead of the Prince. Needless to say, Jemmy is unhappy with this arrangement and longs to escape. One day the Prince hatches a plan to run away from home. Run away from the Royal Palace? I told you he was a naughty one! He bullies Jemmy into leaving with him. And then the trouble starts - they are immediately kidnapped for ransom by smelly criminals. Oh no! Can you guess what happens next? If you were a Whipping Boy or Girl, would you help the prince flee from this dastardly plot? ---- Readers below ten years old would find this adventure an easy read. The vocabulary is simple and so is the plot. Harmless boyish antics leap from each page but never really dip into dangerous waters. Parents may also take this book as a springboard for discussion about running away from home, the dangers of kidnapping, the joy of making new friends, the feeling of being punished for something you didn't do, the health issues to consider before gallivanting with rats in sewers, among other things. Each chapter in this book is quite short that reading aloud three of them a night would ensure exciting bedtime-reading for a week. Also, here's a historical look into the phrase "whipping boy."