Sir Scallywag and the Golden Underpants by Giles Andreae

When King Colin’s golden pants go missing, he calls for Sir Scallywag, the bravest knight in the land. But …Sir Scallywag is only 6 years old and with an evil giant to pursue, it’s nearly mission impossible. With his trusted steed Doofus at his side, Sir Scallywag proves that even the unlikeliest hero can be the bravest knight of all.