I agree, making up verses is perfectly appropriat for chanties, "sailors did it",and it's a great way to get kids involved. Get yourself a copy of Stan Hugills, Shanties of the Seven Seas, or Wm Dorrflingers, Songs of Sailors and Lumbermen. There are Hundreds of choices to work with in both and both are largely clean. By the way, sailors actually sang about booze and women. Isn't it possable to teach kids history, how sailors viewed their world and themselves and still be tastefull yet true to the material?