For home defense?
I have a 6 year old and a 11 month old at home. When I am home, my gun is holstered, chambered with a safety on. When I am at work, it is un loaded, in my safe, in my locked bedroom. Mine is a electronic, 1 foot by 1 foot. Bolted to two walls and the floor.
Why have a gun for home defense if it is not ready to shoot. You may as well have a stick cause all you have is a paper weight.
There's a line between safety and being prepared, but in every case, I believe that when a child is old enough, teach them about the dangers of a gun and teach them to NEVER touch them. As soon as you can, it wouldn't hurt to take your child shooting. Teach them to respect the gun and respect the damage it can cause.