I've been trying to get my 9 year old daughter into programming. She's played Roblox quite a bit and the idea of being able to build her own games is appealing.
The language, Lua, is simple but powerful. We're still in very early days, just had like 2 sessions, but so far so good!
Imho one of the main keys to learning how to code is to stay excited enough to get past the tough parts. That excitement is going to be very different for everybody.
For example, there are people who get really turned on by being able to go low-level / super fast / know what's happening in memory. C/ASM might be the most exciting language for those folks.
Others might love the idea of being able to share what they made with others, i.e. via a website. html/css/js might be a great starter for them
Still others might love the mathematical elegance of type systems and category theory. Haskell would keep them going.
For making something that has cool visual results right away, game engines like Unity (C#), Unreal (Blueprints/C++) could be great. Flash/Actionscript is still a viable route here but not a great investment.
Servers and networking stuff - I suppose python, node, or erlang? If it's specifically web servers, I guess PHP is a good choice too.
The list really can go on and on though... there's niche areas where TCL is probably the most exciting language to build the thing! (actually, when I was a teenager that was the case, I was into writing IRC bots/servers and TCL was great for that)
Where does Rust fit in all this? It has some overlap with all the above (some more than others), it's kindof a bridge of worlds.
I don't think you can really go wrong choosing Rust as a first-language, but it's a toughie. I think if my daughter gets into Lua far enough that she's like really building stuff on her own, I might think of Rust as her second language instead of say C#, Python or JS... but she'd have to have a lot more experience and motivation under her belt before I'd feel like talking to her about Traits and stuff! We're at the level of understanding variables and if/then