I have Mountain Smith packs for both of my dogs that are great. They are 7 yrs old (the packs not the dogs, this is one pack's 2nd dog...) and I still can't find anything better out there. Some dogs can carry a decent amount of weight so this is something every dog owner should look into.
As for my kids (all boys 10, 3 and 1.5)
Bag for my 10 yr old (headlamp, rolled up raincoat, wool socks, windproof gloves, space blanket, lighter, matches, GPS, batteries, pen, pencils, small notebook, granola bars, water bottle) I have his headlamp and GPS using the same batteries, so he only has to carry one size of battery.
I also have a child carrier that has a small bag attached to the back. The 10 yr old may end up with that carrying the youngest, so I have that with his bag in case we need to re-pack him.
Bag for 3 yr old, is the same as listed above, but without GPS and fire starting equipment. Same headlamp as above, so if the boys are together, they can supply each other if needed.
I use these more as emergency bags in my truck than BOB's, but they would serve the same purpose. That's when the eldest would carry the youngest as I would prob have a lot more weight in my pack...