Why doesnt matter now does it? Whoever owns the handgun left it accessible to a child and should be held criminally responsible.
Perhaps you were never a kid nor have attempted to hide a christmas present from a kid.
Short of an armed security guard and electronic thumbprint identification services, a Kid will find and get what he wants.
The solution is that the kid needs to know that he WILL be beaten to within an inch of his life for messing around with it.