A little more info, from GreekChat's resident children's librarian
The author of this series, mostly referred to as the Little Miss or Mister Men books, is Roger Hargreaves. If you travel to the UK you can get a lot more than just books there, they have fun audio tapes! I think I still have my Mr. Happy tape that a friend brought me back in high school from the UK. They've been printed in the US as recently as 1999, and they get slicker with every printing
Google "Roger Hargreaves" and you will find everything you need.