We have the Deuter Kid Comfort III. It is admitedly on the pricey side (it was a gift from my parents) but it is very comfortable both for the adult and the kid. My kid loves being in it, and it carries the weight much better than other kid carriers I've tried. Setriously, your kid will actually feel lighter. It also has a lot of space to carry gear, and a rain cover that is built into the backpack. Oh, and it even has a set-up for a hydration system. Bells and whistles galore! It is light, but the only drawback is that it takes up a good amount of space.

I agree.  The Deuter Kid Comfort II is super comfy for me (I'm 5'3") and my 2 year old.  The seat design is much better than the Kelty for the child, as it covers their entire bottom so they can actually sit as opposed to "dangle".  The camelback feature is great, too, so you can drink water as often as you need.  REI is having a sale right now, so you may be able to get a break on the price.

We've had great luck with the line of Kelty Kids backpacks. Our has lasted through two active boys and many summer and fall trips on the trail, across the park or field, etc. You can get fancy or simple. We've found our model works because it has some storage for critical items like sunblock, snacks, a change of clothes, diapers, water. Also comes with weather protection from sun and rain so the adventure can continue for all! I'd have to say the best feature is the attached mirror that allows you to check on the little one without having to take the pack off disturbing the adventure, or waking him or her up! Happy trails!

I've had a pretty good run (which is still going) with our L.L. Bean model. I don't know the name of it, and it's about five years old, but it's probably fairly typical of their mid-size offerings.

I originally bought this and one just like it in a second color for my kids for school...but they were peanut-sized first graders, so they were a little overwhelmed by their size. Now that they're 10, they're pretty well-matched. The pack itself isn't terribly heavy, and has a well padded back and shoulder straps for comfort. It also has a belt at the waist for additional support, if needed.

It has two big main sections and a roomy bottom area, as well as two outer zippered pockets (one of which has another section to it). One of the big interior sections has smaller pockets for a variety of items. The zippers zip like they're supposed to without catching...always a win in my book! The pack also has a grip on the top and another on the side for carrying it like luggage. The one thing it doesn't offer is an exterior pocket for a water bottle, but we solve that by using a carabiner. I suppose my one other caveat is that with the size of the interior pockets, it would be easy to overload and render the pack a bit heavy, but smart packing will stand you in good stead there.

Expensive but super-worth it has been Osprey 35 lightweight backpack for my daughter when she was 11-13. I can also use it, as she's a tall kid. Large enough to accomodate her sleeping bag, sleeping pad, and 1 change of clothes. Great hip support, light internal frame with breathable panel and really durable-- has lasted 3 years and does not show much wear.