A whole lot of water balloons, or sponges, and buckets of water to keep them in.
On the last day of camp we filled up 2 water balloons for each camper (teenagers) and lined them up in two lines. We made all the counselors and camp staff “run the gauntlet” and the kids got a free shot at their counselors. They loved it!
After the water balloons, for the next camp (kids) we did it we used sponges, and made the kids step back an extra pace or two because the campers were very…zealous. So watch for that.