Agree that good community doesn't necessarily equal large community. I live in Boston, which I believe is somewhere around 17%, and in the central neighborhoods I lived in, percentage of households with families was < 10%. Despite being small, it was a "good" community in that you got to know many of the other families in the neighborhood, I coached local sports, etc. It didn't feel small because of the density of the area AND people were generally on foot or transit and not driving. Running into a family we knew was a daily occurrence. All of those things contributed to making a small population feel much better.

I wonder if there are specific neighborhoods with families closer to the national average?

You say something mathematically precise and then switch into a vague "very few". Take some walks around the parks and go people watching, you will get a better feel for what that "very few" can mean.

13% of 800,000 is about 100,000. Very few.

The crowd arguing with me might say that a bunch of those babies will move to the east bay or similar by school age. And many will. But it's still a very good place to raise kids and grow up.