After you introduce the tradition with edited versions, continue by getting the kids to make up their own verses using a traditional melody, perhaps for work they find tiresome. We once had a class do "math seat work" chanties. Garbage removal or room-cleaning are also popular. If you want to demo some actual jobs, putting them to work with a hawser and block & tackle really helps them "get it". We have also improvised a capstan with some broomsticks stuck into a chair with a rope tied to one of the legs and a large kid as the "anchor". Make friends with the janitor first...

I don't see why they need to hear the obscene or objectionable verses. Historically, most kids would never have heard these. Only kids on board a ship or urchins at the dockside, and they would have been relatively "enlightened".

Most important thing is to convey the spirit of the tradition

Bst- Julia