FWIW Pico-8 uses a modified version of Lua as it's programming language. I would second that (Lua) as a good first choice as that knowledge can be reused in a l

FWIW Pico-8 uses a modified version of Lua as it's programming language. I would second that (Lua) as a good first choice as that knowledge can be reused in a lot of other kid-friendly environments. Edit: ...and later other more practical general purpose programming environments.