I would recommend Python: easy to use, comfortable syntax (the most common gripe / meme is about indenting, I'd say that's a good compromise versus C's arcane symbology, for example..!), rich libraries, you can do anything on a modern OS without a lot of work, granted the performance might not be there, but what are you doing that needs it, and when you do, probably someone's got a library for that already, too.
Arduino, a good embedded introduction, sure. If they're inclined to work with things more hands-on, that's a way to introduce a lot of that from a programming angle.
Javascript, web dev in general: the nuts and bolts of the visible internet. Trivially easy to get into: you're looking at it right now. Show off the capabilities of any desktop browser's dev tools (F12 button usually), and where to get docs (MDN usually). A rather dive-into-the-deep-end to work with DOM and lambdas and all those modern language features that JS contains, but introductions can be structured to ease into that, perhaps following a book or course, perhaps just by looking at stuff. Upsides are it's very discoverable, not like functions have doc attached in the browser (that said, there's probably a plugin for that?), but you can interrogate the properties of any object in real time, and so for example enumerate all the functions (methods) window or Math or Number or etc. have, and look them up separately, and see how to use them right there. Python of course much the same way, when in interactive mode.
I probably started playing with QBASIC when I was... 10 ish? Computer language seems age appropriate, and, anything will do, as long as it's easy enough to make and modify catchy demos on. I'd have likely found these languages much more interesting, certainly more powerful, but also easier to use; there are so many weird quirks and limitations of something like BASIC, who knows what kind of problems I was having with it at the time (but, the online help was mostly pretty good, without which I'd have been hopelessly lost!).
I wonder where Python was all these years... I've looked up hardly any history on it, and only started hearing about it myself ca. college age. It feels much newer than its introduction date of 1991(!) feels. Was there actually a DOS version of it? ...Was it any good back then?
Tim