When my son was 9, we went backpacking in the smokies for 3 nights, during the last week of July. The first two nights, we stayed at the same back country campsite. We took a day hike to Abrams Falls, and we ate lunch there and swam below the falls (with about 20 other people). He loved it. The photos were spectacular. The last night, we hiked to a campsite that wasn't near as nice as the first, but we made do. We got to hear an owl off in the distance and he thought that was awesome.
One thing I tasked him with was getting the water. We use a pump water filter, and after showing him once, and watching him twice, he enjoyed going to the creeks and getting the water. Even was good about keeping the 'grey water' house in a plastic bag and the clean hose seperate.
Stepping away from ultralight, we carried a spotting scope with us on our backpacking trip in Yellowstone. We only hiked and average of 5 miles a day, but loved sitting under a tree, setting up the scope, and using our binoculars to watch the wildlife, while snacking on tortias, candy bars, granola and GORP.
Before each trip, my son and I goto the camp store and I let him pick out our dinner. One thing I will recommend food-wise is measuring out a serving of cereal, and the approriate powdered milk, and putting it all in a ziploc bag. In the AM, open the ziploc bag and dump it all in a bowl, add 1/2 cup of cold water and poof! Capt'n Crunch without milk going bad. I have some powdered milk left over, so I am gonna experiment with powered chocolate, along with powdered milk, for instant chocolate milk. Calories, carbs and refreshing I hope!
Its ironic I just got my son firesteel. He played with it so much, I thought I was gonna be on the news for starting a fire in the wilderness. He also likes to use his Gerger (small leatherman) and sharpen sticks and create kindling. We also pack a small word search book (like you buy at the checkout), pencils, and plastic playing cards (heavier but waterproof).
I also bore him on occassion when I try to teach him LNT camping. He's at the age of actually understanding it.