Agb ... Your concern for the quality of life for your family is obviously a top priority as it should be. All of the communities you are considering will provide a great sense of community and each offers numerous opportunities for sports and club activities. With small children you may still be involved in pre-school. In California these are for the most part private organizations and include everything from Montessori to parent participatory pre-schools.
All of the public schools in the communities you are considering (or have been mentioned by others) have excellent academic programs and credentials. The higher end communities consistently have slightly higher average test scores but that appears to be as much a socio-economic issue as anything else... and all that is great if your children are also achieving at the 99th percentile.
As to communities and what you will get in each for your money here are the October 08 averages: Alamo ($1,630,000), Danville ($949,000), San Ramon ($841,000, Walnut Creek ($853,000), Lafayette ($1,128,000), Orinda ($1,032,000). Obviously, you will on average get more for your $1,000,000 in Walnut Creek or San Ramon than you will in Lafayette, Orinda or Alamo. but the actual product is also different. Orinda and Lafayette were built up in the 50's and 60's and are now known for their large mature trees and rolling hills (though when I was growing up in Orinda most of those trees hadn't been planted yet). Much of Walnut Creek was built in the 70's and most of Danville and San Ramon blossomed in the late 70's and on into this century. From a commute standpoint the distance of your home from the freeway is often significant and so is proximity to the schools. Since most children are driven to school these days the time frame between 7:45 and 8:15 can be a challenge if you are late for an appointment.
In terms of quality of life, the Central Contra Costa area can't be beat. Both my wife and I were raised between here and Berkeley, we raised our 4 sons here and have been delighted with the entire experience. In my opinion you couldn't make a better choice. And if you haven't found your perfect Realtor I would like to apply for the job and put my 30+ years to work for you.
In any event, get your family out here and we will turn you into California natives in just a few years.