In my parks and rec classes at appalachian we've addressed liability in these situations and its honestly a little foggy. In most locales however if they come on your land and get hurt, if you've not acted negligently, i.e. posted signs for hazards and such, you're usually protected if the trespasser has no permission to be there. But again i'm not an attorney.
"Give a man a fish and you feed him for a day. Don’t teach a man to fish, and you feed yourself. He’s a grown man. Fishing’s not that hard." - Ron Swanson