While most of these activities are worthwhile I am not sure they are appropriate for 4 and 6 year old boys.
The six year old may not even be eligible for cub scouts yet. At that age it is very hard to hold a child's attention for long. As a scout leader for five years and a coach for four years I have learned that there is a natural progression of ability, maturity and logic skills that take a while to develop. Not all kids are at the same level either. Better to get them focused on developing good life skills early and work on learning survival skills later. There is plenty of time for that, although it starts to go fast. I would also suggest putting them in sports as well to learn team work and how to get along with peers under stressful situations early. These are much more important skills at age six than how to trap game and start a fire without matches.
Some easy useful things they might be interested from a knowledge base (some of these things everyone knew 500 years ago and no one seems to know today)
- Astronomy, star gazing, recognizing directions etc
- Sign language, either ASL or some other kind of hand arm gestures known only to your family (priceless when someone has to go potty at Walmart, or is uncomfortable but does not want to say why right then)
- How to read, and even draw a simple map
- Observation games like Eye-spy are very useful for teaching younger kids to be observant
- The proper way to identify and plant various seeds
- Acquire them an animal and make them learn how to take care of it
- Read, read, read, read... just about anything is good at that age
- Prepare a simple meal without cooking
- Basic marksmanship skills with BB guns
- Agility races and skills, join in, you might be surprised when they beat you at bear crawling
- Tracking and sign skills during short hikes, more priceless when you startle a deer or a woodchuck
- Plant identification
Make this stuff fun for them and they will be much more likely to go with it, make it a chore and it will go away. Make it hard and they will get frustrated.

