The Whipping Boy — Sid Fleischman

Prince Horace is so naughty that everyone calls him Prince Brat. But the prince is not allowed to be spanked. So an orphan boy named Jemmy is taken from the streets to be the prince's whipping boy.

When Prince Brat decides to run away, he takes Jemmy with him. The boys begin a wild adventure that lands them in the clutches of two thieving cutthroats! Can Jemmy use his street smarts to outwit his kidnappers and free himself and the prince?