I believe it was in the 80's and I can't remember much, but there was a group of boys who were shipwrecked with only one adult, an old man. He later dies and a hermit crab comes out of his mouth. I think that's all I remember thanks

I remember that scene - I think that was this one;

The Blue Lagoon (1980)

There's quite a few references to it being a 'Goof' scene as you can see the guy breathing as the crab crawls out his mouth

Lord of The Flies. Here's an Amazon DVD link.

Amazon.com: Lord of the Flies: Balthazar Getty, Chris Furrh, Danuel Pipoly, James Badge Dale, Andrew Taft, Edward Taft, Gary Rule, Terry Wells, Braden MacDonald, Angus Burgin, Martin Zentz, Brian Jacobs, Harry Hook, David V. Lester, Jeffrey Bydalek,