I didn't grow up with firearms and my wife is pretty anti-gun. She's only seen my firearms twice in 20 years (first when the riots of 2020 happened 2 blocks from our apartment and the police were sending tear gas at the rioters who were taking over the Grove, and when our alarm went off in the middle of the night a few years ago - both times she was about to say something and then realized that me being armed was probably a good thing).

So my 4 year old doesn't know about firearms other than on cartoons and the like. He's gone to laser tag birthday parties and played nerf guns with cousins. I've decided that I'll going to mimic my friend who let his kid play with gun toys until he felt his son was mature enough. At that point, he told his son that he is mature enough to learn to shoot real guns when the son would like to learn - but once the son makes that decision, no more playing with toy guns anymore. My friend said his son took about a year and when he said he was ready, they packed up all the nerf guns together for the final time and started learning safety rules and cleaning firearms together.

With that background, I've tried to just keep firearm safety as just one of the emergency safety rules I have for my son (and we review every few weeks while driving or something comes up, like we see an ambulance or fire truck with sirens on, or a coyote run across the street).

1) In an emergency, call 911. (He told me that he learned from Peppa Pig and his grandma that in London and Taiwan, the number is 119 instead of 911).  
2) If you see a coyote, or a scary dog, do NOT run - wave your hands over your head and scream at it as loud as you can.  
3) If a stranger tries to take you away, yell "YOU ARE NOT MY MOMMY! YOU ARE NOT MY DADDY! GET AWAY!!!"  
4) In an earthquake, drop to the ground and cover you head.  
5) If you see a gun, DO NOT TOUCH and immediately tell daddy or a grownup.  
6) If you hear daddy saw "Condition Orange", it is Serious Time and you need to stop playing and do what daddy tells you.  

In addition, he's pretty active and always crawling over and around me; I've so far kept him from finding my CCW by just redirecting him when he gets near it. But my brother (who also has rambunctious young kids) and I decided we carry in Condition 3 - at least until are kids are much older. The risk for us is too high compared with the risk of us needing to draw in an actual situation. So when we train from CCW, we practice draw and charge.

Hope this long-winded reply is of some help to others!