I agree with Lynn--let them know ahead of time whether or not they should eat dinner. I'm sure the mothers of the boys who are coming are wondering the same thing. Or worse--assuming one way or the other! Then you'll really be on the hook (in their eyes) for not giving better directions.
Do you have to use the grill? My favorite campfire food is "hobo dinner." Have some meats ready (or just choose one; ground beef works great) and have a variety of veggies cut up on hand. Let each boy choose what veggies he wants, then wrap them up in foil with the meat, and a little butter or margarine to keep the meat from getting too dry. Then put them on the coals for 45 mins or so (you might check them at 30 mins; just depends on how much meat you put in the pouch). You could cook this on the grill, too, if you wanted.
You also might have a "spice bucket" on hand; that is, a few spices to let them try. It might be a chance to introduce them to something new. Just have an adult help them so no one puts, say, too much cayenne on his food. Some suggestions: garlic powder, onion powder, red pepper flakes, adobo seasoning (you can promote that one as your "secret" seasoning, and tell them what it is at the end of the night), anything mild and green like oregano or parsley or pizza seasoning (that one won't be hard to sell!).
If you want to go with hot dogs, I'm sure the boys will like it. You might consider a weenie roast over the campfire. Just make sure you have enough roasting sticks. You can make your own or buy some pretty cheap at Wal-Mart.