Minecraft is a well-known, family-friendly game that's available for Mac and PC. It's essentially this generation's LEGO.
Players of all ages can create, destroy, mine, and craft anything they wish in the game using 3D cubes they find while playing.
Some really impressive things have been built in this game. Take a look.
Recently released, Minecraft has over 4 million active players and now has partnered with MinecraftEdu to get kids involved through schools and teaching programs. Kids love Minecraft and it's a great way to let them express themselves creatively.
If you're a teacher and you've heard rumblings of Minecraft and are looking to learn more, I suggest you take a look at MinecraftEdu.