Each troop is different, but our committee is made up of about 10-12 of the more active parents. They also lead trips, and go on trips. In general, parents are helpful to have on trips, because they have cars.
Our scouts cook on their own, set up their own tents, plan their own food, bring their own gear. Parents cook separately, definitely sleep separately, and are supposed to let the scouts do their own thing. They learn from each other, and a big part of BSA is to have the older boys teach the younger boys. Adults without kids can be present on trips, and are usually parents whose kids have moved on from scouting. At no time is any adult alone with any kid except their own kid.
What we have done is have an early season very easy trip, after new scouts have joined the troop from cub scouts (crossed over from cubs or Webelos). I have small backpacks to lend out, and a few sleeping bags. The hike is to a high interest area like a hot springs or water fall, about 2 miles, no elevation gain. Its very doable for 11 year olds. After that 2 mile hike, they think "that wasn't so bad, I think I can do a 4 mile hike, and I want to get a lighter sleeping bag."
Later hikes in the season are increasingly harder, and we have one that is a 4 day, 22 mile backpack that 11 year olds can do. (http://backpackingtechnology.com/backpacking-trips/alice-toxaway-loop-in-idaho/)
The older boys (and their parents) were exposed to a car camping style of camping, and they are not interested in backpacking at all. Don't plan on converting them. But after 3 years of indoctrinating the incoming class of young scouts, and 3 years of older scouts leaving (with their parents), we have achieved a critical mass of backpackers.
More of our trips are on my blog: http://backpackingtechnology.com/
and the troop blog:http://boisetroop100.wordpress.com/