Stumbled upon this article by Marketwatch on the 10 most expensive places to raise a family, and I have to say, I am absolutely befuddled with Washington, D.C. being number one. First off, childcare seemed far far far less expensive there- I had regular babysitters for $14-18 an hour, here in Palo Alto, C.A. I am lucky to find one for $20 as the going rate is about $26/hour. Its an easy browse on UrbanSitter for that data.
Washington also has a bevy of free museums like the Smithsonian and National Zoo providing incredible opportunities for educational experiences outside schools. I think the biggest difference is likely in schooling, you just can't have faith in the DC public school system, while in Silicon Valley we have some of the best public schools in the country.
Having lived in both, with a bank account diminishing far more quickly in Silicon Valley, I find this perplexing... but maybe I'll better understand when my kids are school aged.