We took our twin sons backpacking in Yellowstone when they were 5 years old. They carried Kelty junior tioga framepacks with just a sleeping bag and a change of undies. They weren't very comfortable and it took considerable cajoling, bribery, and competition to get them through it. This year we're taking our 9 year old daughter to Glacier. We tried the REI pack at the store but it just didn't seem to fit well. I finally ended up going with the Osprey Jib, which she loves. It's just a lot more comfortable for her body, due to the excellent suspension system. Again, she'll just carry her synthetic bag, her rain gear, and a few clothes. The weight is not important to me at this point. If she has a comfortable pack and actually enjoys the experience of hiking with it through some beautiful wilderness, I will be very happy, and the groundwork for future trips will be laid. Her twin 16-year old brothers can carry a little extra for her in their Kelty Yukon external framepacks. Meanwhile, old dad here has traded in his Kelty Super Tioga for a Granite Gear Nimbus Meridian and is soooo glad about it.