I like small lumbar packs for children's survival kits. They are roomy and easy to carry. They can be slung over the shoulder (for the smaller kids) or worn on the waist. Many have storage for a water bottle (commercial bottled water size). This just encourages good habits of always having the basic needs such as water, shelter/poncho, light, whistle, etc. It removes the obstacles that people see in carrying a kit by making it comfortable and easy.

I have a more substantial one that I carry and that can be attached to my backpack when carrying that. It is good for all the reasons mentioned above. I also carry a small packable daybag which can take some of the items I may need from my backpack if I am separated from it. There are so many sizes and styles to choose from, you can find one to suit you.

I would not call mine BOBs, just healthy survival kits.