Wow, that's so cool that you and your child can share this hobby and interest together. I'm a front-end dev who has dabbled with open-source game development before, so my advice is going to be a little different than the 'start small and build bigger' and more like 'start with one thing and expand your skill set'.<p>I got interested in graphic design as a teenager, and had tons of UI ideas about the desktop, software interfaces, etc. I also loved video games, so it wasn't long before I was trying to find ways to get my designs into the games I was playing.<p>The first time I ever realized a game could be modded was playing the DOS game Scorched Earth. You control little tanks that shoot each other (like Worms) and when you die they say a quote. Our computer teacher at school had modified the text file to include school-specific quotes and I knew that not every version of the game was like that.<p>Many PC games have active modding communities. I was a young teenager as Quake3 mods were popular, and so I got a really good glimpse at how add-on content can enhance a game. It wasn't long before I got involved with an open-source FPS project (Nexuiz released 2005, now forked and developed as Xonotic). As a 2D artist, I mostly worked on loading screens, the menu UI, the in-game UI, but I met a team of global volunteers from all around the world that became friends. I learned about programming, I got to 'shadow' and understand every role inside a game development team, and I got to have the thrill of shipping a product and playing against strangers inside the game I helped to create! All this before I was finished high school.<p>My advice to you and your son would be to start small with Minecraft mods, or something where you can immediately put the skills you have to use and see changes. This keeps you interested as you learn about and develop skills related to game design you don't currently have (3d modelling, game engine programming, audio engineering, etc).<p>I would also encourage you to contribute or join some open source game projects that are looking for contributors or volunteers. For me this was a social life-saver as a teenager, as well as an amazing educational experience.<p>Best of luck to you and your child, you have a wonderful adventure ahead of you!