Many great suggestions in this thread. Some that I didn't spot:
Lua isn't tough to pick up given you already know JS and Python. It's a bit of a weird hybrid of the two in its own unique ways. If you show that you are learning it with your child, sometimes that can be a great experience. Löve2D can be a fun, very self-contained sandbox: https://www.love2d.org/
On the Python side, Ren'Py can be a great place to start. Visual Novels may not be half as popular outside of Japan, but Visual Novel-like conversations are everywhere in modern games and you can start with easy to script "Choose Your Own Adventure" Visual Novel conventions and expand to a wide range of genres from RPGs to "life sims" to some form of turn-based strategy games easily from there (and just about anything with more work). Ren'Py starts from its own relatively simple conversation-focused scripting language with Python-like conditions, and then allows you to expand towards custom Python code as you get familiar with it. https://www.renpy.org/
Lua isn't tough to pick up given you already know JS and Python. It's a bit of a weird hybrid of the two in its own unique ways. If you show that you are learning it with your child, sometimes that can be a great experience. Löve2D can be a fun, very self-contained sandbox: https://www.love2d.org/
On the Python side, Ren'Py can be a great place to start. Visual Novels may not be half as popular outside of Japan, but Visual Novel-like conversations are everywhere in modern games and you can start with easy to script "Choose Your Own Adventure" Visual Novel conventions and expand to a wide range of genres from RPGs to "life sims" to some form of turn-based strategy games easily from there (and just about anything with more work). Ren'Py starts from its own relatively simple conversation-focused scripting language with Python-like conditions, and then allows you to expand towards custom Python code as you get familiar with it. https://www.renpy.org/