We recently did one night with our 6 year old, 5 year old and 2 year old and it wasn't too bad, and have camped with them when they were younger too. Some tips we learned:
* Try to get them to sleep as close as you can to their regular bedtimes. If you're camping with others that may mean you have to leave the group time around the campfire and get your kids to bed, and then go back out of the tent once they are asleep. Our kids are harder to put to sleep when they are tired, so if we wait too long it can get ugly quick!
* My kids often sleep with a "sound machine" (white noise) at home so we got a battery powered one for the trip to help cover up extra outside noise.
* We have taken a Pack and Play crib when we had a baby that was still sleeping in a crib at home - seemed to work OK.
* We live where its warm, so we just take some light blankets to put over the kids when they invariably wriggle out of their sleeping bags.