I didn't want to talk about whether a child should or should not have access to the gun because I believe that's a subject that the parent should make the call on. I've met 6 year olds who were more responsible with firearms than many 12 year olds. This was about the subject of putting a gun within relatively easy reach of a child. If something tragic were to happen, do you think the prosecutor will give a pass to those who put a gun in a child's room because they thought the child was mature enough? Not a chance, they're going to hang that person out to dry.
My parents would have called me a responsible child. They never really had firearms in the house, but I knew what to do if I came across a gun. But they still fascinated me. I had a buddy in high school who also would be considered responsible. He had his own .243 that he hunted with by himself all the time. That didn't stop him from figuring out the combo to his Dad's gun safe and showing me all the guns they had. I don't ever remember doing a chamber check on any of those guns, yet I held each one. That also didn't stop my friend from raiding his dad's stash of black powder (also under lock and key) and us playing with it. I distinctly remember one incident that left the garage full of smoke, and him and I running out coughing. Some of the stuff we did was really stupid, and we were "responsible" teenagers. Our parents never new the stuff we did, and we're very lucky we have all our fingers still, and didn't put any new holes in things that didn't have holes before.
If you feel you need to put a gun in a child's room, do what you feel you need to do. My kids are 4 and 1, so it would be trivial to put a safe on a top shelf in the closet and they wouldn't be able to get to it, at least not for a couple years. But as a parent, it's my responsibility to keep my kids safe. I don't trust a small, cheap safe to keep my kids out. They'll figure it out eventually. Do what you need to do to keep your family safe. I know the best way for me to do that is to keep guns out of their reach (for now) and prevent unsupervised access as much as possible. The easiest way to do that is keep all my guns in the floor safe, and a gun on me at all times.