Almost all the trips I go on involve taking less experienced people hiking, and planning for multiple people other than myself -- really ups the stress level and planning, since there is that added challenge of helping to ensure that people have a good/great first experience.
A few things I'd recommend; some of this will echo folks above:
* Talk to your friends in the area and get their gear lists -- not just the stuff they use, but the stuff they don't use, so you know what you can borrow. I know the basic gear for all of my friends with any backpacking inclinations -- in fact, I've started keeping a lot of this info on my own master gear list, with their initials beside their gear, so I know who has what that I can borrow if I need to.
* Pick a LEVEL campsite. For a lot of people, sleeping at an angle is one of the biggest challenges to camping when they are starting out. They can slide around, become disoriented, have a hard time sleeping, etc... Level, even if it's not as smooth, is my pick for new campers.
* Sleeping pads -- Since you're looking for LEVEL ground as more important than smooth ground, make sure you have really good sleeping pads to smooth out the lumps. In my experience, when people can get comfy and get a good nights' sleep, it does wonders for their experience.
* Campfire -- go somewhere you are allowed to build a fire. Campfires are probably the most favorable, nostalgic icon for camping. If your planned trail/site doesn't allow fires, then pick somewhere else.
* Campfire FOOD - bring a few things that will cook really well over a campfire. One of my favorites is to get pre-cooked turkey sausages from Trader Joe's. Freeze them the night before, wrap them in a camp towel and freezer ziploc, and they will unthaw in the pack during the day. They are ready for the fire at night -- just put them on the ends of sharpened sticks, roast them, and serve them in small whole wheat pitas (light, compact, resilient). Bring along tiny condiment packages if you think they're needed. Great campfire food is a lasting memory for everyone, and it's an experience unique to camping. Along the same lines, a few marshmallows are worth the space -- especially if taking a 10-year-old along. One other thought: small apples, while heavy, are oh-so-tasty when roasted over a campfire. Again, IMHO it's worth the weight.
* Plan to allow the newbies to help with everything. Given them some basic principles and then let them pack their own backpacks. Let them help set up the tents; show them how and use it as a teaching moment. Let them blow up their own air mattresses. Let them choose and sharpen their own sticks for the fire... you get the idea.
* Good socks: make sure everyone has smartwool or something similar. Good socks = happy feet = happy hike. Fresh socks for day two are worth it.
* Camp shoes: if the folks you are with have shoes they haven't hiked much in, then allowing/encouraging them to bring flipflops, crocs, or some other lightweight camp shoes can add wonders to their overall comfort. 8-10oz for a pair of crocs is totally worth it if it means you can relax by the fire for the evening, can move safely around camp, and don't have to try to get tired/sore/blistered feet back into boots until the morning.
* Pants/shirts -- to a lesser degree than socks, pants at least help with the experience. If they don't have any hiking pants, then encourage windpants or pretty much anything other than jeans/cotton. In the event of rain, you want them to not be miserable.
* Games/cards/lantern -- these extras can be worth packing, especially if weather is iffy. If there is any chance you will spend the night stuck in a tent together, then a lantern and something to do together is worth the weight.
* headlamps -- plain and simple, headlamps are cool tech toys, easy to use, and empowering. If everyone has one, it helps independence and comfort. at ~3oz. each, they are worth the redundancy.
* maps -- everyone should have a map with clear notations on it -- where you parked, where you will camp, and the route you are planning to get there. small compasses for everyone are nice, too, just in case.
* bring an ACE wrap or athletic tape or something similar so that in the event of a sprain or other injury you can make it as easy as possible to help them out of the backcountry.
* Bear bag explanation and pack check. I've found that new folks often leave things in their bags that could attract a bear. I've never had it happen, but a worst case scenario is that a bear ransacks a first-time-campers tent looking for the half-eaten trail bar they shoved in the small pocket of their pack and forgot about. Make sure to explain bear safety and to have each person go carefully through their packs to make sure anything that has had food on it, all food-related trash, and other scented semi-edibles like toothpaste are bagged like they should be.
* I'll echo that ipod/earlpugs can be worth their weight in gold for people new to the wilderness.
* GPS -- obviously, not necessary, but for the cool factor, if you've got access to some kind of GPS, it can be fun to see and track your exact elevation gain, rate of travel, how far you've gone, all that stuff. it makes it easy to answer "how much farther" and it also provides a way to have some follow-up content in addition to photos after the fact. You can e-mail or print out for them the exact route you hiked (along with any sidetrails) and the elevation chart for the trip. can be fun and make it more engaging for some people. I had a hike recently where we decided to bushwhack down the side of a mountain and it was great looking at the almost mile-long stretch of decent down a 60* slope.
* plan a great meal for the end of the trail en route back to home. Know that you'll have your favorite restaurant as a payoff is a great way to keep going on the trail and to feel like you've earned a big dinner. it also serves as something to look forward to when the steps are getting slow/tired late in the hike.
* Accept that it is unlikely you will be going ultralight this trip. When new people are along, I normally end up carrying more than my share of the gear, along with some extra gear for an expanded safety margin for the group. I often end up with a 35# pack with several newbies along; that's okay with me if they have a great time, and with first-timers on the trail, the distances are much shorter and the pace is slower, so I really don't mind the extra weight.
Sorry for the long post, but I hope some of the suggestions are helpful.
I wish you well in your hike. One of the reasons I backpack is because I enjoy introducing new people to the sport/lifestyle. It's a lot of work, and it means I keep some extra gear in my closet, and I will unlikely ever be a truly ultralight hiker (at least not consistently), but the payoff is worth it.