I was four years old the first time I fired a BB gun; that gun had been given to my brother for his fifth birthday. He carried that gun everywhere with him every day after school and used it to shoot those little toy plastic soldiers, blackbirds, and on one memorable occasion to have a BB gun war with the kid next door. (Dad nearly killed him when I tattled, that's why it was memorable.)
The first time I fired a .22 I was probably around age 7. Maybe a bit younger, maybe a little older. The .22 lived in a soft sided case under mom & dad's bed, unloaded. Dunno where they kept the ammo.
I did not realize they even owned a handgun until I was in my teens. Dad showed it to me and taught me how to load and unload it before he & mom left me overnight by myself the first time. They kept it loaded next to their bed in a well hidden drawer.
My kids (ages 10, 8, 7, 6, 4) all know that I have a handgun. That handgun is kept locked up or in my holster at all times. They have each had a chance to hold it when it was empty and know that (almost) any time they ask, I will unload it and let them look at it. Double safety: it's locked up and I've disarmed some of their curiousity. Of course they know the safety rules too: the oldest ones know the Four Laws and the younger ones know "Stop. Leave. Get an adult."
The older three have fired a BB gun and the older two will probably be given a .22 for Christmas this year.
Hope that helps.
pax
"A boy becomes an adult three years before his parents think he does, and about two years after he thinks he does." -- Lewis B Hershey