Most kids die from exposure. I'd strongly suggest they carry some kind of "shelter" with them too. A 33 gallon plastic trash bag is compact and simple. Bright orange ones are great and are likely available from your local highway department. If lost the boys should tear a face-hole just below one corner.

Go through Doug's Survival for Kids section on equipped.org with the boys. Have them practice putting the bags on.

The most important thing for them to know is to carry their kit with them at ALL times when "in the field" (it won't do them any good if they don't have it), admit that they are lost, stay put, and make themselves "findable". The most important thing for leaders to know is to be willing to call for professional help sooner rather than later.