Curious what draws you to the AT, versus anything else? While iconic, and certainly beautiful in spots, it sees a lot of traffic.
When our girls were 11, and our son 15, we did the 33 mile Feldtmann Loop in Isle Royale NP, in 4 days/3 nights. While my son and I had a little backpacking experience, my girls and wife did not. Only saw a couple of other hikers, and a ranger, the whole time out. A very special place. Most hike the length of the Island on the Greenstone Ridge Trail, getting dropped off and one end and picked up at the other, but that is a bit longer, and a lot more traveled.
http://www.summitpost.org/feldtmann-loop/260525