Why does my Macbook Air get so hot when playing even a simple game?
Although the games may not be graphically intensive, they may still be intensive on the CPU, and it is likely the CPU temperature you are seeing rise. 

A way to check this would be to use Activity Monitor.app while playing a game to check out the CPU usage. Or if you are comfortable and able, SSH into the Mac while playing the game and using the top command to check.