Hi @Skipper_of_Stones, we’re the parents of a 3-year-old boy. Here is what we do anticipating possible emergencies (we live in earthquake country). He has a bag with him at all times. It has his name in it: It also has pens and syringes along with a vial of insulin, which lowers blood sugar, and an emergency glucagon kit in case his blood sugar gets dangerously low to the point where he is unconscious and cannot intake sugar. It also has a blood sugar meter, a lancet and test strips, alcohol swabs, a bunch of glucose tabs and glucose gummies, jelly beans, a charger for his cell phone (which transmits his blood sugar data to us, the parents) and his Dexcom receiver. If we were going camping, we would add to his emergency supplies: a spare sensor to read his blood sugar every 5 minutes in case the one on his arm goes bad, a spare pump site and reservoir and skin tac and unisolve wipes (the pump site is for kids who use pumps), the latter two are to make things stick to the skin and to remove sticky things. In addition to this, we have laminated notecards with simple instructions that will keep him basically alive and out of DKA in the event someone else has to take care of him at daycare and he gets stranded. It shows basic insulin doses for food, basal insulin, and how to treat lows and treat an emergency hypoglycemic episode.
While it’s important to understand how blood sugar is affected by various foods, most diabetics nowadays are told they can eat whatever they want as long as they take the appropriate amount of insulin for it. This would be particularly true for a 5-year-old, because they’re growing you can’t really restrict what they eat to regulate blood sugar in the same way you can for a 50-year-old. If they’re camping, they’d be eating camping food. In a survival situation there are probably a lot of unfamiliar foods and foods where you can’t figure out insulin doses precisely.
Our precocious 3-year-old is pretty on top of things. But here’s where I diverge from some of the other commenters on what is possible for a 4- or 5-year old at this age. They *may be able to test their own blood sugar, though that’s not super likely…but would be extremely unlikely to be able to give themselves insulin injections, and they would NOT know how to count carbs or figure out the dose of insulin they need for specific food. They would be able to understand that when they’re low they need carbs (and would probably know the rough amount of sugar they need to treat a low – say 3 jelly beans or 1 glucose tab), but they wouldn’t be able to reliably self-treat as that would require them having the self-control not to gorge on an available supply of sweets. They might be able to feel that they’re low (which may make them feel shaky, sweaty, look pale and dazed and confused, but also very hungry. My son tends to trip a lot when he’s low, and if he’s really low, he gets super shaky and wants to eat everything in the house). But sometimes my son confuses the sensation of being low with being hungry, or with being high, as some of the symptoms overlap. In general, he would be able to articulate how he feels but would not necessarily be reliable indicator. So if you didn’t know his blood sugar and you had to rely on his word, you could maybe get in the ballpark some of the time but you’d be off a lot too.
Also, I have to say I’m a bit skeptical of the notion that responsible parents would send their 4-year-old off into the wilderness with only a minimally-trained uncle. So you’ll probably have to send a grizzly bear along to kill the parents off on the way or something like that – we don’t even leave our son in the care of trained caregivers who are more than 10-minute walk away 
!
As for things that could affect BG in a survival setting. Well, simple infections like colds or ear infections can raise blood sugar, make people insulin-resistant and lead to a condition called DKA, and high blood sugar can delay wound healing and make it hard to fight systemic infections, so if he sustained any kind of wound or cut that would be very tricky to handle. Then, exertion and altitude can lower blood sugar because both require more aerobic respiration and may increase insulin sensitivity – yet at the same time intense exercise can cause DKA even at low or normal blood sugar because the muscles can take in sugar when exerting themselves, but other organs, like the kidneys, can’t, leading to a situation where certain organs are starved for insulin/sugar while overall blood sugar is low. Stress hormones can spike blood sugar, as can growth hormones. Snake bites or venom can trigger kidney failure much more quickly in someone who is diabetic. Starvation could trigger DKA, dehydration could trigger DKA. Vomiting can be really dangerous in that setting because it means you take insulin for food and then can’t get your blood sugar up. And without means of monitoring, its easy to imagine a person going into a hypoglycemic coma overnight. Lots of scary situations to imagine…
