Five kids, 9yr, 6.5yr, 5yr, 3yr, 6mo.
No loaded long guns or revolvers, though I have a few loaded magazines, all ammo except for 1 mag is stored separately. All stored out of reach, all in cases. With my kids I don't feel the need to lock the cases.
My wife's Kel-Tec P11
was stored loaded (w/o round chambered) on a high book shelf by the bed, and the S&W 411 was stored with a loaded magazine in a pistol box (which the kids are not strong enough to open) out of reach, and none of them are strong enought to rack the slide - yet.
Then I got an XD-40. I deemed it not safe to keep loaded with one in the chamber (too easy for kid to manipulate the safeties and pull the trigger), but since I bought it as my primary HD weapon, I wanted to keep it "condition 1" so to speak. So I bought this for $25 at Wal-Mart:
https://www.honeywellsafes.com/sites/prod_detail.cfm?product_id=32
Now the XD and the P-11 reside in the box, rounds chambered, in Kydex holsters.
My kids are taught Eddie Eagle style as soon an they can understand. The 3 yr old isn't ready yet. On average it happens somewhere around 4-1/2 years. When I have been shooting the three oldest ones are apt to ask if they can see/hold the guns, which I always allow them to do, and every time we review Eddie Eagle, then it goes something like...
"What do I have to do before I hand you a gun?"
"Check if it's loaded."
"OK, let's check." (go through steps for that particular gun) "Is it loaded?"
"Nope."
"What do you do when I hand it to you?" (later, when they are able, I will add "don't trust me, check it yourself" to the list)
"Point it in a safe direction."
"OK. Where are you going to point it?"
"That way?"
"OK. What else?"
"Don't touch the trigger."
"OK. Here you go."