As a Police Officer, there was no way my kids weren't going to see my guns. We had a standing rule. Want to see one of my guns? Ask. And, they did. I would unload it, we would handle it, make sure to remind them not to point it at anything they weren't willing to destroy etc. Brief course in how to handle it, clear it, load it etc. Told them, anytime you want to see any of my guns, just ask. Want to go shoot them? let me know, we'll go to the range. Really, its no big deal. Don't touch them without permission, but, they are there for you to look at, handle and shoot any time you want to. You see a gun unattended, let me, or another adult know. Don't mess with it. You're at a friends house and they want to show you thier dads gun, tell them no and tell them if we go back to our house, dad will let them handle it AND shoot it any time. Its no big deal...k?
After a few weeks of "Can I see your gun?". It just faded out. It was just another thing around the house, like the blender, the saw, whatever.
I would occasionally test them. Leave an unloaded gun, within eyesight, on the coffee table. One of my sons would walk by and say: "Hey dad, your gun is on the coffee table..." and, thats it.