First of all, bravo to the parents for training their children what to do in such a case, and bravo to the girl for doing it.
Secondly: I used to live in Los Angeles. The law there (not sure if this is city or state but whatever) is you have to lock up your gun unless it is within arm's distance for you to use for self-defense. Given the crime and homeless issues there, I had it within arm's length (in a makeshift gun purse) at all times when I was home, and because normal people do not get a carry permit there, locked it in the safe when I left. So I got in the habit of locking it up when I left the house. Now I thankfully live in Arizona. I live in a very low-crime area and this house is well-secured, so I leave the house gun in the bed holster when I'm home. I could still get to it in time in case of an attempted break-in. It's too big to conceal carry, so I got a smaller one for that purpose, but I still lock up the house gun when I leave the house. I would probably lock it up if I were getting a visit from folks with children. If a worker is coming over to do something not in my bedroom, I don't lock it up. IMO the best reason to lock up your guns when you're not home is to prevent theft. Besides the fact that you would not want to have to re-create your collection, I'm sure no one here would want their guns used by BGs to commit crimes, which is the inevitable result of theft.
Tangent: If anyone is interested, I did a lot of research on gun safes when I became a gun owner, and concluded that the Fort Knox ones were the best of the ones on the California list. (Yes, not only your gun, but also your safe have to be on a state DOJ approved list. I think it's just a way for the state to get money because a lot of the ones on the list were featured in the video a few years ago of gun safes being easily opened by 3-year olds.) The FAS-1 appears to be made the same way as the Fort Knox ones but wasn't on the Cali list so I couldn't legally have used it to lock up the gun when I wasn't home. However a person with small children could have one bolted to their bed frame for night time if they have a listed one for storage when they are not home.