One, here are two lists of online games to teach coding, first list is for CSS, other is for WebDev. Frankly, I've bookmarked them for myself, they look so cute.
https://dev.to/paco_ita/train-your-css-skills-with-online-ga...
https://dev.to/paco_ita/train-your-javascript-skills-with-on...
Two, why not set your kid up with PyCharm, and start dabbling together with Python. (like build a simple chatbot or something that pulls stuff from Wiki).