I let my son go through the "feel and fondle" process with a 1911 when he was four. He agreed that it was too big for him. The deal was, when he thought he was big enough, we'd go let him shoot.
He got his first Daisy Red Ryder at around age six. He had been given safety instructions and a warning about what would happen if he got careless. He had a minor Oops! and it got wrapped around a tree trunk. I gave him another one for his birthday, a couple of months later, and apparently he'd had the original lesson driven home.
Other shooting occurred along with size and age and all that.
What's important, seems to me, is to remove the mystique and any "lure of the forbidden" from the whole gun deal. If a kid sees guns as normal parts of life, tools for specific purposes, you've gun-proofed the kid. You darned sure can't kid-proof a gun.
Art