As like you, I'm "teaching" my coworkers (primarly apprentices) and I'm hitting the same spot. With 10+ years of experience with strong types languages and as far as I love JavaScript its kind of style I would not recommend JS for teaching fundamental knowledge. Showcasing maybe since "if" or "while" are quite common across the languages.
But (and since I do not know python that well) JS has its, sometimes rough, edges (e.g. "this" context) which becomes more a disadvantage for the trainee. In school often Java is used (since the in the ones my apprentices attending) since its low effort apporach (no heavy IDE necessary) and it is a very widly used and accessable language.
But I think C would be also a bad choice. It's way less accessable and has more than enough edges. To be fair back in the day there was way less choice what language to take than today.
But what I also notice is that "manual memory management" becomes a niche over the time. Don't get me wrong, I don't say it would go away. There will be always a low-level layer to program to. But measured against the amount of developers and it's different profession "targets" it wil become less. As comparision (please don't hit me :) ) the automatic transmission. 20-30 years ago it was less efficient than a human. Today it's the opposite. I think in memory management on an application level we hit that road too. We’re not quite yet there (Electron anyone?) but we'll getting there maybe in the next 10 years.
So in the end what's the right choice? I have no absolute answer. It depends also on the environment the trainees are in. In my case JS is a mandatory but not the only one so I try to teach as language neutral as possible and also let my trainees do stuff in other languages. Surely they have to be flexible.