Some of the tricks to pull on adults while going camping include take a water bottle, unscrew it so that it leaks a little bit of water, and set it in their sleeping bag. You may as well smear shaving cream on the adult hand when they are asleep, and then tickle their face.
A rubber snake. Or tie a piece of string low on a bush and run it back to where you sit at the campfire. Tug on the string after dark so they think something is in the bush. Just remember to take the string when you are done as it can be harmful to wildlife.