During my summers in Idaho as a child we had such fun adventures. One of our absolute favorite memories at Grandma's house was our twilight pillow fights. My siblings (there were four of us) and I would all get our nightshirts on and each get handed an old pillow. After the sun went down my mother and grandmother would just sit on the front porch and watch us go at it out in the yard. We would just nail each other over and over again and surprisingly enough, there were very little tears shed over the course of the years. There were a few rules and there were set boundaries (you had to stay on the grass), but there weren't too many restrictions. We would hit each other so hard we would fall over and once you had fallen you would get attacked by everyone. My mother and grandmother would just laugh and laugh and occasionally they would throw a pillow or two.
We would have our pillow fight for a good twenty minutes to half an hour. Until we were nice and exhausted. Then we would brush our teeth, say our prayers and go to bed.
You might need to set some more ground rules for your families/cousins/friends like no hitting in the head and maybe there could be an optional safe zone where you could go and not get hit.
Gosh, just thinking about this again makes me want to go out right now and nail my brother Travis in the head with a pillow.