I think the only answer is yes. Not everyone is "sue-happy" but all it takes is one person. Of course, no one wants anyone to get hurt.
I also don't know how clear cut the lines of ownership and the associated liabilities are when a property line goes through a body of water.
ewest gave a good presentation very related to your questions. One of the things he suggested was to carefully consider all of the areas where you are exposed even if they seem so remote, and then protect yourself from all of it.
If you've granted permission, you've started to connect the dots to yourself as a responsible party.
Are there lifeguards, safety devices, etc. etc. ?
Don't get me wrong, I'm not trying to rain on a parade. On the other side of the coin, it's a very nice thing to do for some kids.
