Ok, a bit more time now, so an answer more fitting to the original question.
Taking it for granted that keeping a safety on, until ready to fire, is one of the fundamental rules of gun safety I can say the following: there is no dilemma even if a gun does not have an external safety. In that event any internal safeties and the safe gun handling of the person touching the firearm is what keeps it on safe.
Now for a more important part of the discussion. The students you are teaching about firearms and about how to shoot NEED TO ABSORB CERTAIN INFORMATION BEFORE EVER TOUCHING A GUN OR SHOOTING IT.
You said this:
I think the idea is to give the pupil a memetic device, if you will. They are absorbing a lot as it is. What would you reccommend I tell them?
To which I will say this: if the potential shooters are not fully familiar with all of the rules of gun safety, they should not be picking up a gin at all. If you are bringing someone to the range to shoot and, you have not yet taught them all of the rules of gun safety making certain that they understand them all, then you are making a big time hurry up mistake that could cost a life. There should be absolutely no range time without first having assured that each of the people about to shoot are familiar with those rules.
Rules I would insist upon would be as follows (there are some others too but these are mandatory):
1) Alcohol, illicit drugs, many prescription and, many over the counter drugs do not mix with gunpowder. Make sure to impress upon your students (which is exactly what they will be) that they must be in full control of their mental and physical capabilities while handling firearms. It is a shame people do not always place this as rule number one.
2) Treat every firearm as if it were loaded.
Side note on #1
a) You will need to explain that if someone picks one up, has one handed to them, to keep it pointed in a safe direction, then while keeping finger off of the trigger to check it to see if it is loaded before doing anything else with it. If they do not know how to check a particular gun, then have someone else do it and show them or, just do not touch it.
B) You need to show, then teach with hands on, someone how to check each gun they are about to fire - before they fire.
3) Whenever you handle a firearm make sure it is pointed in a safe direction (yes this actually includes when you are about to justifiably and legally shoot someone - think about that - a dilemma if ever there was one).
a) This will require some explanation as what some people think is a safe direction is asking for trouble. The safety of any direction in which a firearm is pointed depends on whatever scenario you are in at the time.
4) Keep your finger off of the trigger before you intend to fire.
a) This one really has to be hammered into their heads and yes there are exceptions to this rule such as when preparing to disassemble certain pistols and rifles. So you also have to tell them if they ever need to put the finger on the trigger for any reason other than shooting, they absolutely have to go to rules number 2 and 3.
5) Know your firearm and, know how to use it, before attempting to use it AND make certain it is in proper operating order before using it. (This always holds true except in emergency situations.) Also maintain your firearm in proper working order.
6) Make absolutely certain to use only the correct ammunition in your firearm. (Ammunition is varied, yet many are so similar they can fit into various guns; so I make this a separate point and do not blanket it in under 5.)
7) Use proper eye and ear protection except in an emergency. Make sure all others in the area are also wearing proper eye and ear protection if you are shooting for recreation.
8) Know you target, and be aware of what is beyond your target. Also be aware of anyone else in the area while shooting.
9) OBEY ALL COMMANDS BY RANGE PERSONNELS. OBEY A
CEASE FIRE COMMAND FROM ANYONE AT THE RANGE.
a) This last one is for old timers as well as new people. It needs to be drummed into new shooters as do all of the above rules. As a matter of fact it is a good idea to remind old timers of the rules now and then.
Every time you teach a new shooter, you should teach them these rules. This should take at least 45 minutes to an hour before any gun handling. Then comes some teaching about various types of firearms (typed by action and longarm versus handgun). Then some gun handling to see how they are handling the firearms and to give them some hands on info, feel and confidence about the gun(s) they will be firing. You should teach them hands on, about the particular gun(s) they will be shooting, before they shoot. Again, look to see how they handle the gun, how well they took in the gun safety lecture you just gave them and so on. look for accidents waiting to happen and correct them, also praise good habits in the making.
Now go out onto the range. Explain the layout to them. Explain range etiquette to them. Explain the regular range commands, explain the firing line and other range terms. Explain CEASAE FIRE and proper actions to take if this command is given. Explain what to do if they have a problem with a gun. For example they have a jam. Tell them to keep the gun pointed downrange (hopefully you explained terminology to them already), finger off of the trigger, then raise the off hand - just like a kid in school. Tell them never to turn around while on a range if there is a problem or if they need to ask a question, again remind them to raise their hands.
Just about ready to shoot. Keep in mind, you should not allow more than three of them (two is much more preferable and one is best) to shoot at one time per each instructor watching over them (each shooter on range positions set up right next to one another). In your case, I believe you said, you will be there with a fairly new shooter and two completely green potential shooters. You should have them standby and show them a few shots you take. Then have each one shoot a few shots, one person at a time while the others remain behind the firing line, and well behind you the instructor, as they watch. A few rounds each, maybe 5, then onto the next shooter. Then do this again another time or two for each of them. Then you will have the feel for them and they should have the feel for the instructor, rules, the guns and firing them. Then you can have all three shoot while you instruct from behind them. You should never, I SAID NEVER, shoot at the same time a brand new to fairly new shooter is shooting and you are the one instructing said shooter.
Teaching firearms safety and shooting to others is a big responsibility. Do it right, so they get it right.
These are along the lines of what I would do, what I have done, and how I learned to shoot from others who have taught me.
Best regards,
Glenn B