How can firearms be secured from children, preferably without locking them away in a full size safe where they would be completely inaccessible in an emergency?
For babies and toddlers, setting it on a high shelf should be sufficient. Also, choosing a pistol with a grip safety is a great move -- little hands simply don't have the span to hold it down properly while pulling a trigger (as opposed to "thumb safeties" which are buttons or switches easily manipulated by small hands before firing). Additionally, unlike thumb safeties, trigger locks, etc. a grip safety does not increase the time it takes to bring the firearm to bear in the emergency.
While your child is very small, it is important to teach firearm safety. In homes where this is done properly and consistently, the child(ren) in the house don't need to have guns kept away from them, because guns have no mystery any more, and the child(ren) understands the consequences of mishandling, he/she/they will have no urge to use them improperly.
Here's what we did with my (now 8yo) son:
From birth, my son was accustomed to tactical knives, firearms, and other weaponry as part of everyday life. When he was born, we lived on the military base where my then-husband served. I'm a practicing martial artist (and now, so is he).
When my son was a toddler, I made a point of leaving training knives (rubber mock-ups of my tactical knives used for sparring practice) within his reach. My son was allowed to touch them and even pick them up, but only when he handled them with all the care due real blades, something in which I instructed him regularly.
When my son had the rules down, I began leaving my real knives out from time to time, surreptitiously observing to be sure that they were handled properly.
By the time he was three years old, my son could be trusted around blades of any kind. He asked before picking up a "sharp knife" (i.e. butter knives, putty knives, etc are safe without asking), and when he did use any knife he kept the blade away from his body, cut away from people, and was careful of surfaces that could be damaged. He NEVER treated a knife like a toy.
At four, my son began cleaning firearms with my brother and father, learning how they work, etc. He's seen them fired (and what one can do to an angry coyote).
At five, my son began studying martial arts.
I'd like him to have begun learning marksmanship by now, however my son has hypersensitive hearing, so until we are done building an outdoor range at my parents' home, he won't have the opportunity to do so.
Responsible use of weapons (be they fists, knees, feet, knives, guns, swords, or anything else) is one of the basic values my son was raised with. It is re-enforced daily by our Sensei, by me, by my extended family, and by the other adults in my son's life. That is more powerful protection than any mechanical measure ever devised.
The best advice I have heard is to teach your child how to safely use guns as early as possible. This takes away a lot of the curiosity that gets kids in trouble and teaches them how to properly and safely handle a gun if they ever come across one at, say, a friends house.
Beyond that, if you want quick access for emergency use only, then a trigger lock should be sufficient. Or a small easy to open combo safe by your bed.
I'll let you know what the foster care regulations are for the state that I live in, then adapt them to something more usable.
In order to assure perfect safety, a firearm should be protected by several layers. This include:
Now, if you are worried about safety, but also the time to access, you should most definitely keep the ammo stored in a different place than the gun. Storing a loaded gun just makes it far too easy to do anything. Also, perhaps some practice with getting the gun ready to use, preferably at a difficult time like at night, would be a good idea, so then you can store the gun safely while still making sure you have enough time to get the gun in an emergency.
In addition, it is crucial to teach kids about gun safety from a young age.
In addition to education, you should consider whether there is an alternative to a firearm for fast-response emergency situations. For example, pepper spray can be quite effective in case of home invasion, and if a child finds and uses it on him or herself or someone else, they will recover.
Alternatively, you can try to require a less-fast response: if you put a gun safe in a bedroom or other centrally located room, you're more likely to have time to open it; a burglar alarm or automatic lights can give additional warning, etc..