Camping with happy kids is wonderful - camping with miserable kids could convince you to pick a new family hobby.
There's lots of ways to ensure a happy camping experience, but here are my picks for the three most important.
1. Keep the sleeping bag dry. Let's face it, sleeping comfortably is pretty important to all of us, but a wet sleeping bag can make a kid totally miserable. This is especially true if your child's sleeping bag is one of the big box store $20 variety. You know, the ones that weigh 15 pounds (dry!) and are made of cotton. Get one of those wet, and your camping trip is over, it will take until next year to dry. Even a good kids sleeping bag can get wet, however, and it's not easy to convince a kid to climb into a soggy bag to sleep.
The key to keeping a sleeping bag dry is to keep its surroundings dry. If you're going to be in wet conditions (rainy season, or paddling on a lake), prepare your gear. Put kids sleeping bags, and any other gear you treasure into dry bags, garbage bags, or some other water barrier. Put a tent cloth under your tent (properly!) so you keep water out of the tent. Teach your kids good tent etiquette so they don't crawl all over the tent in their wet boots, or dump a mug of hot chocolate over their sleeping bag.
2. Avoid constipation. Think I'm kidding? I used to take city kids on month long canoe trips, and several of them showed insane talent for "poop in the woods" avoidance. Some made it as long as a week before they gave in and took Mr. Trowel off to dig a hole. Kids like routine and predictability, some kids a lot more than others. When that routine is turned upside down, even by fun activities like camping, it can cause system backup. That can lead to stomach troubles, cramps, and really stinky farts (amongst the 2-12 year old set, this is serious business, and might be for you too, if you're sharing a tent).
Fortunately, there's a really easy fix for camping constipation. Eat beans. I used to serve chili the first night out on trail. Vegetarian chili with 5 kinds of beans. Sometimes it took a day or two, but no kid could hold out a week against my 5 bean chili. Other forms of fiber help too - oatmeal for breakfast, dried fruit in your gorp. Also have your kids drink lots of water, especially if fiber isn't a really common part of their diet.
3. Don't take over. We spend most of our lives "organizing" our kids, making sure they get up, dressed, off to school, to weekly activities and play dates. It's an easy trap to try to organize their camping experience too. This is especially easy to do when it looks like their first choices of activities involve sleeping in the tent all day or throwing rocks at one another across the firepit.
However, one of the most fundamental lessons camping can teach is that you are responsible for your own experience. Mother Nature is a great provider of natural consequences. Don't put up your tent right, you'll get wet. Don't collect firewood, you won't eat hot food. Do collect firewood, and discover the mesmerizing dance of a night campfire. Get up the energy to paddle to the middle of the lake in the middle of the night, and see stars like they were meant to be seen. Step back, and let your kids learn from their own experiences. You might just pick up a little something too.