Thanks for coming back and explaining what you're looking for! Here are, hopefully, some answers to your questions. For explanation, I'm the mother of 4 and grandmother of 6. I try to take the three younger grandkids (currently ages 7-12) out backpacking several times a year. One grandkid at a time, though, unless their father (my youngest son) comes along!
My own pack is a single large bag with three outside mesh pockets. It's a smaller version (since discontinued) of the
Six Moon Designs Starlite, with added "optional" stays. I pack so that nearly all of what I need during the day is in the outside pockets: snacks, water bottle, water filter, rain gear. My insulating clothing (in case it turns cold) is inside but right at the top where it's easy to get to, with the first aid kit (the only other item I might need to access) just under it. The only time I've ever had to get into the bottom of my pack during the day was when I fell during a difficult stream ford and had to dump several inches of water out of my pack (my critical insulation was in dry bags and didn't get wet). Of course then I had to empty the whole thing out!
As I mentioned previously, with the many pockets on standard kids' packs, my grandkids inevitably forget which pockets the water bottle and snacks are in and have to open three or four to find what they want. I've been thinking of labeling the pockets! They and I would both prefer a lighter, simpler pack like mine (single pack bag with outside mesh pockets). With mesh pockets, they can see where their snacks and water are! They learned early on to pack what they need during the day where it can be easily reached without unpacking the rest. They have also learned to treat their packs gently and not drag or throw them around.
Nearly all packs built for young children weigh 2 1/2 to 3 pounds. It's really disgusting that when the weight limit for a 9-year-old child should be no more than 9-10 pounds, a quarter to a third of that is the weight of the pack itself. Children's packs need to be made simpler and lighter without sacrificing the needed support structure. This could easily be done by leaving off the gewgaws and many pockets and using a lighter fabric (such as Dyneema, which is just about as bombproof as the extremely heavyweight coated nylon used in most children's packs).
If I could sew, I'd cut the pack bag off the frame/harness of a Deuter Fox 30 and make a simple Dyneema pack bag to incorparate the frame and harness. The Fox 30 is a wonderfully supportive and comfortable and fully adjustable pack for elementary school children, but it weighs 2 3/4 lbs. Getting rid of the gewgaws, multiple pockets and heavy zippers, plus substituting Dyneema for the overly heavy coated nylon, would cut at least a pound, maybe more!
Even the youngest child (that's of 4 children and 3 grandchildren) always wanted his own pack, although for preschoolers it contained only a fleece top, rain gear, small water bottle, the day's snacks and a small stuffed animal. If they needed help, I (or their parents) took out part of what was inside, usually when the kid's back was turned. It was a matter of pride for the kid to carry the pack the whole way, even if (unknown to them) it was nearly empty!
My personal gear list is modeled after this one on the home page of this site:
27-pound, 7 day gear list. (My gear is now a bit lighter than that; 25 lbs. for 9 days.) This would vary according to the part of the country and expected weather, but works fine for me in the high Cascades spring through fall and for the northern Rockies in summer. With young children, the main difference in their list is that they need a complete change of clothes--if there's any water around, they'll inevitably get wet!. Parents (grandma in my case) carry all the shared gear--tent, cooking pot and stove, food, water treatment, first aid, etc. My grandkids started carrying their own sleeping bags at age 8; before that Dad got to do it. Next summer when the oldest grandson is 13, he'll be able to carry part of the shared gear as well as all his own!
You might want to read this article:
"Hiking with Children" by Penny S. as background info, since you don't seem to be very familiar with the process.
As mentioned, this is a lightweight backpacking site, so most of us are quite concerned about the weight we have to carry. A 25-lb. pack is the absolute maximum I can carry, and I prefer not to exceed 20 lbs.
I'd personally like someone to investigate the commercial possibilities of a simpler and lighter children's pack, with support structure (including adjustable torso length) similar to the Deuter Fox 30 but the entire pack a pound lighter, rather than adding even more weight and complexity to an already overly-heavy pack. It could have multi-colored fabric and logos to be appealing without adding to the weight. Elementary school children, younger Scouts and other youth too young for adult packs would be the market.