I strong encourage keeping kids packs as light as possible. A 60 pound child shouldn’t be carrying more than a 15 pound pack, and I think it would be best if the pack was closer to 6lb. A 100 pound child shouldn’t be carrying more than 25 pound, and I would recommend keeping it below 9lbs or so. Notes about backpacking with kids are on another post.

Conventional wisdom is that people should carry a backpack that’s <25% of their body weight. This is reasonable for moderate distances but will be fatiguing on a longer hike. There were several experiments run various militaries. A key finding was that on an all day exercise trained individuals had a measurable increase of fatigue and a drop in agility when they carries more than 10-12% of their lean body weight. This matches my personal experience: I feel no more tired at the end of a 20 miles carrying 17lb as compared to carrying no pack. My one caveat that when over 8 lbs I need to shift some weight to my hips or shoulder pain will be fatiguing through the day. My wife found her sweet spot is around 6lb.

There are a number of factors which effect selection a pack for kids which aren’t a factor for adults:

• Growth: Kids are going to grow.  If you want the pack to fit for more than a year you need to get a backpack which has an adjustable torso length.  External frame packs tend to be highly adjustable.  Deuter, VauDe, Osprey, and Kelty each make at least one kids size internal frame pack with a highly adjustable suspension.
• Durability: In general, kids are pretty hard on equipment. Most kids are not sufficiently careful to use packs made from materials such as light-weight sil-nylon, so you really want a pack body to be made from a durable material such as Dimension Polyant, Dyneema, or Cordora.
• Peer Pressure: Some kids like to be trail-blazers / thought leaders. For these sorts of kids, getting a pack which is different and in some way better than the standard is appreciated. Other kids want to have the same pack as everyone else, and will be terribly embarrassed being different, even if different is better.
• Enforced sharing:  Boy scouts typically share equipment, food, etc. This means that even if all your child’s personal gear is ultra-light, the group might end up bringing 8lb tents, cast iron dutch ovens, etc, and you will need to take your fair share. So unless this is troop which has embraced ultra-light techniques and gear, you kid will most likely want to get a pack designed for mid-weight packing.

Daypacks:  For very young children, Eagle Creek made a really great daypack, but it has been off the market for awhile.  There are countless day pack / book bags available for kids today. A florescent Barbie or shockingly bright Barney backpack might not blend into the back country, but there isn’t really a need to buy a special pack for hiking… use whatever backpack goes to and from school since they are already use to carrying that pack. In fact, kids might be happier with the bright color backpack, and you might as well since they are easier for you to see. I was very amused early on beause my daughter didn’t care about any of her gear other than it’s color. Originally she really liked “Red”.

Backpacks: For smaller kids, there are only a few pack which have a torso short enough, a waist strap which can be tightened enough, and has enough volume for all their gear (need at least 1800ci).  For example, 1850ci has just enough room inside it for a North Face Tigger sleeping bag, a Big Agnes Insulated AirCore mummy sleeping pad, a 1L platypus, her clothing  for a three season trip, eating utensils, toiletry kit, flashlight, and her smallest cuddly. Even more volume would be required if the kids is fully self supporting or carrying their fair share of group gear and food. I realize that adult ultralight backpackers can easily get down below this volume, but most kids gear will be higher volume because items like kid size 800 fill down sleeping bags are not a good investment. Most kids will not be as careful as adults, and items have a limited lifetime because the children will grow. It makes sense to purchase less expensive items such as sleeping bags made using synthetic insulation.

For young kids (say <11y) I would suggest checking out the following packs:

• Any daypack/book bag: Use whatever backpack is used daily for school books. Fill the day pack with whatever will fit without being too heavy (I would recommend keeping their pack under 10 lbs). Carry the rest of their gear in your pack and have a great time.
• MLD Prophet: (size XS). Rob used to make a size XS which was great! Seems like he only goes down to size S now which is for people 5’1″ or so. My daughter used one of the rare (and no longer made) MLD kids packs.
• Deuter Fox 30 (torso 10-17″, 2lb 10oz, 1,850ci, $79): Very comfortable for most kids (though one girl who borrowed it didn’t like it). The torso length is easily adjustable with a pretty wide range as does the hip strap (goes down to 22″). Good size for kids who are carrying their own gear, but adults are carrying food and shared items. Very durable material. Two side pockets and top pocket provide some organizational features. Back pocket and side mesh pockets are close to useless. You can strap a pad on vertically running ties through the retaining straps for the top lid.
• Kelty Junior Tioga (discontinued now, torso 9-14″, 3 lb 6 oz 2050ci): External frame pack for small kids.
• Osprey Youth Series: A number of full featured packs that weight ~3-4lbs.
• Tough Traveler: Makes a number of internal frame packs for kids. I have never seen these packs, but there have been a number of recommendations from people on discussion lists.
• ULA-Equipment Kids Packs: Excellent packs
• DIY: Make your own backpack.

For average size children older than 11 years old  I would also consider any classic ultralight or light weight packs that have short torso models.