"it" is really a personal choice, and Santa Monica has plenty of choices to chose from... My kids got to Edison Language School, which I found to be an amazing community of diverse backgrounds glued together in their interest of Spanish language and Latin American Culture,... something that I believe will benefit my children greatly in their future professional and persona lives given the Los Angeles demographics. They also have a pre-school program.
Another great pre-school I am familiar with is Mount Olive Preschool which is second to none.
Many in Santa Monica feel Grant or Frankling elementary school are the "it" schools... they are very good schools, but not the "it" for me, but they may be for you...
The best thing is to visit, and interview people and follow the advise of people in your network of personal relationships as they may reflect your own set of values and priorities better.
Santa Monica in general is a very cosmopolitan and fascinating place with many "it" for many people.
Best of luck!