> the only people having babies in Silicon Valley are seemingly Indian and Chinese, along with a smattering of Mexicans and other immigrants. I have a bunch of white friends here, and of the ones who have had kids or are planning to in the near future, they fit into two groups: 50% have moved back to their hometown already, and 50% are planning to.

I have a feeling that you are seeing there a hyperlocal trend influenced by the particular local demographics. In the east bay from Oakland and north and in the mid peninsula, SF, and the North Bay, there are a lot of white families with kids (along with the other demographics you mention except perhaps fewer Indians)