You said that BSA's policy is don't eat anything unless you're an expert - or in a desperate situation. To a child, a "desperate situation" could be going without food for a day or two. There are plants that you can simply touch to your tongue and immediately remove it and risk going blind. Eating some plants, though not deadly, can cause severe diarrhea, as I'm sure you know - which in a survival situation can be very debilitating, if not deadly.
Someone told me about the "Rule of 3's" - You can last 3 minutes without air, 3 hours without shelter, 3 days without water, and 3 weeks without food. Although it isn't entirely accurate, it's a good way to remember the priorities.
There's an organization in San Diego called "Hug-a-Tree" that was started by a woman whose 9-year old son was lost and died overnight from hypothermia, in about 40 degree weather, as I recall. She started this organization and teaches children to "hug a tree" in an effort to keep them in one place so rescuers don't have to go on a wild goose chase trying to find a kid who keeps wandering.
So much other stuff... This is a subject I am passionate about, lostproofing children. Every child I come in contact with, if I can, I teach the basic rules of both staying found and then what to do if they get lost. I wrote an article about it at http://www.associatedcontent.com/article/1822631/lostproofing_how_to_prevent_your_child.html?cat=11. There's another one on "What Your Child Should Do If Lost in the Woods" at http://www.associatedcontent.com/article/1713723/what_your_child_should_do_if_they_are.html?cat=25.
It's a wonderful thing you are doing because if not for you, these boys might not ever get this knowledge. Keep doing what you're doing! It's so important. If there's ever anything I can do to help, please let me know.

That is so cool! I've always been interested in how to survive with basically nothing and as an adult have taken a number of wilderness survival courses and ended up teaching it at a kids' summer camp I was fortunate enough to run for 7 years.
Do you get into the uses of plants as well as their edibility? What about different ways of preparing plants? That is wonderful that you are passing on the information.

Also, if you like the wild edibles group, you might like the wilderness survival group.