Here's how I did it with our two young sons (who are now grown and hold CHLs).
First though, I confess to having started their safety training with a teeny weeny fib.
Only after the first one asked his first question about guns, I started as follows. I opened the gun safe and let them look inside, and invited them to examine anything they wanted to handle, (which turned out to be all of 'em!). Once they selected something I pulled it out, went through the safety check (magazine clear, CHECK. chamber clear, CHECK!) during which I explained what I was doing and why. I then explained the "every firearm is loaded" concept which led to the logic of the "finger off the trigger" and "muzzle in a safe direction" rules.
After they were satisfied I closed and locked the safe. I then said, "even though we TREAT them like they're loaded, it is a fact that the firearms locked inside the safe are all UNLOADED. So, you see? All of the guns that are locked away in the safe that you can't get to, will not hurt you. First, because you can't get your fingers on the trigger, and second, because they are unloaded. It is the guns OUTSIDE THE SAFE that will kill you. Or your brother. Or your friend. Or the neighbor across the street. So, if you find such a weapon, DO NOT TOUCH IT! If you want to handle it, wait. Come and tell me. I promise I will drop what I'm doing, make it safe, and then let you handle it, or even take it apart."
The teeny fib (big fat lie?) was that when they were growing up, I never ever left a weapon unsecured, loaded or unloaded.
During that first lesson I went through several scenarios such as "a friend comes over. You want to show him an unsecured weapon you've found. He insists on picking it up. Tragedy strikes and a young person dies. The boy who lives, lives with a pain that will never go away." I was pretty graphic. Since that wasn't gonna happen at OUR house I then went through some scenarios of what they should do if a similar situation should come up at A FRIEND'S HOUSE!
Finally, I imparted my own philosophy on firearms: They're just a tool. They are neither good nor evil, smart nor stupid. It is the person holding them in his hand who is one (or a combination) of those things. I then pointed out that not everybody shares my philosophy, and that most people, as seen on TV, either demonize or glorify guns.
Every "lesson" was with both boys together. The entire first lesson and tour lasted not more than 15 minutes and satisfied their curiosity for years. When they were a little older (about 8) we started making trips to the firing range. They quickly became deadly proficient with single shot .22 rifles. Later, pump, then autoloader .22 rifles. After they were a little older still, I let them fire a 7.62x39mm SKS (ONE ROUND AT A TIME. I would let them load one, chamber one, and fire one, frequently reminding them of not only the fine points of marksmanship, but more importantly, the safety rules. After they were older still, I let them fire .38 and even .44 special revolvers. By that time, they pretty well knew all they needed to know. A little while later, I let them fire autoloaders - ONE ROUND AT A TIME! Load one, chamber one, fire one. Then two.
By the time they were fully grown they were fully competent with all actions. Today they can outshoot me, easily. They, my wife, and I, all hold CHLs.
That's how I did it and it worked. They went at their pace and, over the course of their childhoods and adolescence, got fully up to speed. It's particularly satisfying to me, not so much because they SHARE my philosophy, but because they arrived at it, through their own intellectual reflection and processes. They are competent with any action. But they are as "fascinated" with guns as they are with a crescent wrench or a hammer.
Not saying it will work for you. But it worked for me - and them.
Best,
VT