My son is three. I keep all of my guns besides my primary defense/daily carry gun locked in safes within a locked and keyed closet. My primary gun is kept on my person except when I am sleeping. When I am sleeping I keep my primary gun holstered in my nightstand. I installed a hidden latch that prevents my son from opening the drawer if he suddenly becomes interested. At this point this is a sufficient safeguard but you have to be vigilant because kids figure stuff out quick.
As far as talking about guns, I started talking to him as soon as he started really talking. He now knows that he is not allowed to touch guns and that they can hurt you. This is a good start, I think, and as he gets older I'll expand on the education. In addition, my wife and I decided not to have any toy guns in the house until we are sure that he is old enough to comprehend the difference.
The main thing is restricting access to the firearms. Your kid will be curious, my son asks me all kinds of questions about the gun. Now he tells people Daddy carries a gun, he shoots targets.