Thinking in Terms of Learned Hand's "Formula"

A couple lives in a hostile neighborhood.  Unknown persons throw rocks through their windows.  There are other acts of violence, accompanied by threats.  The couple buys a pistol and stores it a drawer at the top of a six-foot-tall cabinet.  Trigger locks are available, though not easy to find.  They cost $50 and take four minutes to remove from the gun.  Son and daughter-in-law, with their four rambunctious children aged 6, 8, 10 and 12 visit regularly.  One of the children takes the gun from the drawer when everyone is in a different room.  Are the gun owners negligent?  Is it a matter of law or a matter of fact?  How should we analyze the question?  Which facts are relevant to which variables?  Does it matter which child gets the gun?

Consider each of the following variations:

1.  Child falls and pokes her eye out with the gun. 

2.  Child falls and shoots playmate. 

3.  Child points it at a playmate and, not thinking it is loaded, shoots. 

4.  Child purposely shoots playmate.