[legion]

My son is 3. I would never put him alone in a room with an unsecured loaded gun.

That said, I've been training my son since he was 2:

If you see a gun:
-Don't touch it.
-Tell a grown-up.
-Leave the area.

When we were looking at houses last year, he stumbled on an M1 Garand in an unlocked closet. I was right behind him and couldn't see into the closet. I saw him open the door, his eyes got big, and he backed out of the closet and yelled: "Daddy, there's a gun in there!" I told him "good job" and gave him a huge hug. The whole rest of the day I made a point out of praising him for listening to daddy and doing the right thing.