I tell anyone with kids (my friends, my kid's friend's parents, etc) that I do a lot of woodworking and I've got a lot of sharp-edged tools around the house. I ask them to please call ahead rather than drop in unexpectedly so I can make sure my tools are put away.
I've taught my kid not to touch guns he or others find. If he's at a friend's house and the kid gets a gun w/o parents present, he's to leave immediately. He also knows the Four Rules and how to unload most common firearms.
I also am more than wiling to let him look at my guns under my supervision. This prevents guns from being an object of curiosity. If he's at a friend's house and his friend says, "hey, let's check out my Dad's gun" I want him to think, "Big deal, I can see my Dad's guns anytime I want. Let's go ride bikes instead."