I personally wouldn't include the juice boxes or electronic devices. Maybe homemade juice powder and a canteen of water, make sure the beverage is safe and healthy. But civil unrest and natural disasters are supposed to be bottle-necking events, pruning the overgrown human population down to the strongest and/or smartest. Apes shouldn't need video games for morale to survive.
Okay, to be fair, I have a handcrank USB charger JUST for my mp3 player and Nintendo DS.
For adults, a backpack should be no more than a quarter of your body weight. Smaller gear can be carried on upper limbs to better distribute weight. For small children, like before puberty, a backpack should only be between 10%-20% of their weight. And something flat or soft (like a folded tarp or blanket) should always be packed in the backpack against the back.
For kids 4 years old or younger:
Members of the group take turns carrying them in a harness or cradle-board. Toddlers are too slow on their feet, especially for quick getaways. Some basic gear is kept in small bags that clip onto the baby harness for quick access, like clean diapers or a little baby first-aid kit. Anything else the toddler needs is carried by the parents who chose to reproduce.
I don't think 6 is young enough to start learning primitive skills. Then again, primitive living is more of a lifestyle for me, not just a skill or a hobby.
I agree, a lot depends on the child's skill level, and how much weight they can safely carry. Food should be the comfort item of choice, healthy wholesome food that provides both caloric energy and the proper nutrition for bone, brain, dental, and immune health. A handheld game or plush animal won't hurt. I have several dozen plush animals in my trailer....
I think 4 is old enough to learn basic first-aid. Within reason, of course. No small child should use a syringe or scalpel unless they have prodigious skill, thorough training, and urgent need. But bandaging and cleaning wounds are basic skills every kid should learn early. A kid can also be taught to filter water, tie knots, build shelters, find heartbeats, check breathing, and find help.
Ever notice that almost all kids love building pillow/sheet forts, curling up in boxes, and/or playing in tents? That is our natural animal instinct to build or find shelter. For about a million or so years, humans lived as just another thread in the food web, and we evolved to regularly seek new shelter instead of living in a big house built by someone else. Those instincts express themselves through child's play unless the nature is squeezed out of them.
Ages 4-6
*Blanket
*Clean Clothes (could wear some of these instead of lugging in a backpack)
-Breathable Bandana/Scarf
-Breathable Boots With Good Grip And Wiggle Room For Toes
-Beanie Or Sock Hat
-Fingerless Gloves (For Finger Freedom) And....Finger-Mitten-Cap-Things? (For Warmth)
-Heavier Hooded Jacket/Coat
-Long-Sleeve Shirt Or Sweater
-Short-Sleeve Or Sleeveless Shirt
-Socks And Underwear (more than you think you'll need)
*Compass (teach them to use the sun, moon, and stars too)
*Cordage
*First-Aid Kit
-Anesthetic/Antiseptic Salve (eco-friendly and edible, just in case)
-Bentonite Clay And/Or Charcoal Powder (for snakebites or other poisonings/infections)
-Certain Other Kid-Safe/Required Medicines
-Cotton/Other Hypoallergenic Bandages
*Snacks/Spices (perhaps based on body type and genetic heritage for maximum efficiency)
-Dried Fruits And/Or Vegetables
-Dried Honey, Maple, Or Sugar Crystals
-Fatty Nuts/Seeds (Cocoa, Coconut, Hemp, Poppy, Pumpkin, Walnut; DHA For Brain)
-Hard Dry Cheese
-Herbs/Spices (immune-boosting or infection-fighting; prevents mold, pests, rot)
-Lean Jerky (Wild Game Like Deer Or Turkey)
-Sea Salt (Or Other Naturally Sourced Salt)
-Starchy Seeds (Amaranth, Flax, Plaintain, Quinoa)
-Sweet Beans (Like Carob, Hopniss, Licorice, Or Peanut)
-Whole Grains (Brown Rice, Emmer Wheat, Rainbow Corn, Wild Grasses; NOT Genetically Modified)
*Stainless Steel Water Bottle/Canteen
*Water Filter
Beginning Ages 9 To 11 (Puberty):
*Clothes
-Bra Or Sash (for girls, to prevent bouncing boobs; it's hot to see but not to feel personally)
-Maybe Groin Protection For Men?
*Fire-Starting Kit
*First-Aid Kit
-Basics Like Antiseptic And Bandages
-Herbal Contraceptive (Blue Cohosh, Neem, Western Stoneseed, Wild Carrot Seed)
-Herbal Spermicide (Aloe, Lemon, Mint, Pure Live Yogurt)
-More Potent Medicines (If Properly Trained)
-Suture Kit (And Possibly Certain Surgical Tools) If Properly Trained
*Knife (Possibly Other Weapons)
*Sea Sponges Or Cotton Pads (washable, reusable, sustainable; for girls on their menstrual period)
*Water Distiller
This is all totally on an individual basis though. Just like adults, every kid will have different preferred and required gear based on skill level or simple choice. If a child begins studying and practicing young enough, you'd be amazed what they could accomplish between toddlerhood and adolescence. But some things are better safe than sorry.