My 12 year old son adores this game and needs to have his fingers pried off the keyboard. The game itself contains no bad language, or indeed any language. However there is the possibility of exposure to older players and their uncensored commentaries when your child visits posts from this game on YouTube.
I would recommend being careful allowing kids on a public server, but the game can be played solo, and a smart parent with the resources could set up a controlled server, for the child to play online with friends. The game allows perfect gameplay in a nearly limitless world of imagination. It is not unlike giving a child a box of infinite blocks which can be changed and altered to fit the needs and desires of the child. Kids can’t choke on it, just be sure to limit how much time they play.
This excellent independent title is an wonderful educational opportunity for tweens and teens, with the ability to build and construct it fosters creative thinking and problem solving. All positive. On the other hand, exposure to an online community brings privacy concerns as well as exposure to the creations of others, which may not be appropriate. Know your child, discuss that others on the internet may make inappropriate creations in the game or use foul language, and discuss with your child how to handle such a situation. Also be sure to discuss privacy and not giving out real name or location.