I've been playing Minecraft with my son (also 8) since he was 4. There is so much in there that can be used to teach them if you're also involved. Not just math, either. My kid is currently writing a story in a book in Minecraft to work on his spelling and I'll jump into his world from time to time to read it and help correct some spelling and punctuation. It's very important to limit the time, especially at their young age, or they'll get too attached.

There's also Minecraft Education which we play around with sometimes. It's got a number of lessons available for different subject, but also good for you to design your own lessons. It also does a good job getting them into the basics of coding using a little robot they can program in the game and build whatever they want.