Python is a great option because it is high-level, easy to pick up, powerful and has a library for anything they are interested in pursuing. Something like streamlit is cool because you can write a small amount of code to build a useful web app that you can interact with. For data viz related things, Jupyter + Python (maybe Pandas, not SciPy or NumPy unless that sort of math is specifically interesting to them)

Javascript and webdev is also a decent option since you can build such interesting and shareable web apps quickly, but the frameworks and scaffolding can be intimidating and painful.

I would work backwards from a project/interest and pick a high-level language where it's easy to get a good enough solution and create something that feels like an accomplishment. I would want to teach both programming as well as the joy of programming.