keep the ammo separate from the guns
I think the biggest thing is keeping the ammunition away from the guns, I'm 19 now, but I remember when I was really young like it was yesterday,lol( like 2-3yrs, too young to understand gun safety), I was able sneak away from my mom for a few hours to always find my dad's guns and i'd look at them and stuff, but there was never any ammunition easily accessible so shooting them, or loading them never crossed my mind. My dads ccw was always on him, or in sight. The fact of the matter is that no matter where you hide them/lock them up, the kids will eventually be able to find them and get them. I was picking locks by the time I was 5. You've got to remember that kids have an unbelievable amount of free time to do whatever they want, so it is not unreasonable for them to sit there and push the buttons on a combination safe for 3 hrs, or look for where you've written it down, or find the spare key, or whatever, they will get it open eventually if they want to. The big thing is not keeping them loaded, or keeping ammunition near them, after all, a 2yr old kid isn't going to know that you can't put the 30-06 round in the .38 special. From personal experience, it's pretty safe to say that they won't be able to put two and two together if the ammunition and guns are stored separately. Of course, I was shooting .22's and stuff with my dad by the time I was 4 or 5 , so by then, it wasn't a big issue because I knew gun safety, and knew not to show my friends the guns. (one time i got caught showing my friend "my" .22 when i was 6 and boy did I never do that again, I must have had a hard time sitting down for a week,lol)