This is why I always tell people - it's easier to gun-proof your children than it will ever be to kid-proof your guns.
Think you've hidden it well enough they just won't find it? You're kidding yourself. If they know about it, they WILL find it. Didn't you ever look for Christmas/birthday gifts as a kid? You know you did. Did your parents know that you'd found them? Not always, right?
Even at 3 years old, a child can be taught that a gun can be dangerous, and should never be handled without supervision by an adult. The NRA's "Eddie Eagle" program preachs "Stop - Don't Touch - Leave The Area - Find An Adult" as what children should do when they find a gun somewhere.
Not to say that guns shouldn't be locked up - they most definitely should if not in your direct control (in a holster on your person). But mechanical devices - be it a safe, lock, or the safety on a gun - can fail, and should not be depended on as the only means to prevent a tragedy.
Education is the key to safety.

What is the point of rules that are not enforced?