Good question. Here's a quick answer - Read and Practice.
1. Borrow or buy the Boy Scout Handbook and read Second Class Scout requirement 2c.(page 77-79 of the edition I have). Better yet, buy the Wood Carving Merit Badge.
2. Ask advice and questions of local scout leaders "Say could you show me how to do this?", "How should I teach...", "Could you recommend..." Be prepared for different opinions on knives, sharpening, wood. There may be a training class at Roundtable or University of Scouting. A woodcarver or Woodcarving Merit Badge counselor, and maybe your den chief or another Boy Scout are possible resources.
3. Buy or borrow a basic, lightweight pocket knife which fits in your hand and has a short whittling blade (smaller than the main cutting blade). No bulkly, ten-tools in one knife.
4. Count your fingers before you start and have a box of Band-aids handy.
5. Follow safety rules, particularly the safety circle. Test knife for sharpness - does it slice (sharp) or tear (dull) paper? If dull, sharpen. Never test knife or chisel sharpness with any part of you!
6. PRACTICE whittling a simple neckerchief slide or whatever you want to carve. Small cuts away from you. Take your time.
7. When done, count your fingers again. If the number is the same as before and you are on your way to becoming "qualified".
I did not teach knife safety until my Bear den demonstrated consistently that they could follow our posted den rules. Around April, they have achieved that goal and were ready to learn a new set of rules - Knife Safety. We started carving soap and then basswood neckerchief slides to be worn for their Webelos cross-over. Had a couple of finger cuts which were quickly bandaged. Overall, this worked well.
Here's the Knife Safety rules that my den proposed. I was pleased that they had obviously read their Bear book and surprised that the first two rules that they came up with are NOT in the Bear handbook.
1. Always have adult permission and supervision.
2. Always know where to get first aid.
3. A knife is a tool not a toy.
4. Know how to sharpen a knife. A sharp knife is a safer.
5. Keep a blade clean.
6. When not using your knife, close and secure it. Close the blade
7. Keep your knife dry. Oil as needed.
8. Before opening a knife make a safety circle.
9. Make easy, shallow cuts away from you. Let the knife do the work.
10. Never throw a knife or cut a live tree.