I've started my 3 1/2 year old son with the Eddie Eagle rules. I make sure he knows that they apply EVERYWHERE, whether it's at a friend's house, grandpa's or uncle's house, if he sees one laying around outside, etc. He has been repeatedly told that he is never to touch a gun unless 1) I say he can, and 2) I am right there next to him.
I have also tried to dispel the mystery of "daddy's safe." If he asks to see, I'll stop what I'm doing and show him. I'm hoping that this will limit his motivation to explore. While he is handling any firearm (always under my direct supervision) I work on the three basic safety rules (don't touch the trigger, don't point it at anyone, etc). After I put everything away and close the safe, our next stop is to the bathroom to wash our hands thoroughly to remove any lead/oil residue.
While it might be a little harsh (especially remembering myself at a young age), we don't even allow him to play with toy guns or pick up a stick and pretend. Again, that may be a little over-restrictive, but my wife is a closet anti- and this keeps the peace between us and avoids more restrictive edicts like "he's never to see another gun again." I don't want him to have to figure out why it's bad to play with a real gun but a toy gun is ok.
As an additional layer of protection, I put a rubber band around a little key tag with the words "Gun Safe" on it inside the safe. When the safe is open, I keep the rubber band around my wrist to remind me that I need to close it again in case I get distracted.
He asked a few days ago if he could go to the rifle range with me. His maturity level won't support that yet, but it's got me thinking about some airgunning. I'll have to see how that shakes out with the wife...
