I use pico8, which I really enjoy. It’s an all in one environment that runs portable so it can save a few headaches!
It’s very 8-bit, but I find this keeps the focus on code.
Students can graduate onto full Lua or Love2D if they outgrow it.
Here is an open source version that runs straight in the browser so should work great across Chrome books 🙂
Some of my level 6’s use Unity, we also use Blender – lower students can wire up 3D games in seconds and advanced students can code it with Python.
If you intend on introducing students to Unity I like to use https://playcanvas.com/ as it has a similar workflow, without worrying about set up and running lots of separate apps. ( Should also work on Chromebooks )