I wouldn’t worry about missing one dose, even if it is the one most needed because these medications given do stay in the body for longer than the dose is given so as soon as you have the next dose is taken your levels will be on track again. I wouldn’t be too hard on your son’s friends parents because it isn’t that they aren’t responsible but because they aren’t as used to remembering medication like you, even though i’ve been on medication for 14 years theres still 1 or 2 times where i go 1-4 hours late and suddenly  think, MY TABLETS! You could help your son to remind them too just by say if he has a watch set the alarm to whenever his dose is needed at night then he can stop and ask them for them. This is what i had to do as a younger kid because my friends parents forgot too. Don’t make too much of a thing about it to your son because as i found my mum sometimes was TOO worried and i found her coming on school trips with me because she didn’t trust the teachers and it was really embarrasing to be honest, i know she meant best but travelling to the local farm just incase i don’t take my tablets and if i fall over, that i may need an injection i found a little over the top. She only allowed me to go on a french trip for 3 days when i was 11 because my teacher had a diabetic son so was good at remembering. It’s much easier when he starts remembering and when he’s old enough for a mobile phone..It is worrying i know but missing one dose is ok so don’t worry too much:)