I think it's good training to suggest they contribute with their snacks and drinks. Maybe you could also suggest they help build campfires and grill some cowboy packets or burgers/dogs with your supervision. I loved doing stuff like that as a kid.
I'd also suggest dividing up a few chores like dishwashing and trash removal, as an educational experience. You have a great opportunity in a relaxed, fun setting.
This is fresh in my mind because we just spent our 40th annual multi-generation week at my brother's beach house. Some of the "Kids" are now in their forties, and don't do much to contribute or seem aware of the cost to my brother of hosting them (lost rental that week, cleaning fees, linen service, utilities, etc.) They didn't get the right lessons as teenagers in how to be a good guest.
The "Kids" (not mine) make big salaries, drive expensive cars, own all the expensive electronics of course, etc etc. We four old siblings are all retired and watch our pennies. None of the kids prepared a meal, emptied the dishwasher, bought groceries, even glanced at the check in a restaurant on their parents anniversary, etc. They ran off to go boating or up to their oceanfront rooms to read, leaving a greasy popcorn pan, pizza boxes, empty water bottles etc on the table. Meanwhile, us old people, cooking dinners for 15, have a variety of disabilities that come with age.
At the end of our annual gathering, two of us proposed hiring caterers next year. One of the kids (a Vice President of a major corporation earning six figures) said, sort of pitifully, "Would we all have to share in the cost?" Yes.
End of rant. I applaud the original poster's plans.