Renee Watkins is worried that something is missing from her quiet street, lined with single-family homes in the Berkeley Hills. Families.

Even though Renee lives just a few blocks from an elementary school, she says she rarely sees kids in the neighborhood.

“Where I live, I’d say half the people are over 70. Perhaps I’m exaggerating, but it’s amazing how many people are old. And on the other hand I see hardly any children,” she says.

Renee’s partially right. There are more elderly people in her neighborhood than children. In 2017, about 31 percent of the people who lived around Renee were 65 or over and about 17 percent were under 18, according to data from the U.S. Census Bureau.

The number of children living in a neighborhood varies dramatically throughout the Bay Area. Although San Francisco is known for having very few children, the Bay Area as a whole is not that different from other major metropolitan areas. Contra Costa County has the largest percentage of children in the Bay Area, while Santa Clara County has the most children, according to U.S. Census Bureau data.

Where children live in the Bay Area has changed over the decades, but the percentage of children as part of the population has not drastically changed since the 1990s.

People with children are looking for single-family homes, says Cynthia Kroll, the head economist at the Association of Bay Area Governments, and those homes tend to be in the suburbs.

Demographics and affordability tend to impact where in the suburbs families are moving at any point. For instance, right now there’s a shift happening in older neighborhoods, like Renee’s in the Berkeley Hills.

“There are many parts of the Bay Area where older households are still living there. People are aging in place, they haven’t moved elsewhere,” Kroll says.

When older residents do leave their homes, new families are moving in.

“Someplace, like Marin County, is actually starting to inch up in the proportion of children they have total in their population,” Kroll says. “They have been one of the oldest counties.”

But a lot of families can’t afford to live in Marin, even if there is a growing housing stock there. Affordability is a major reason there’s been an increase in families in places like Contra Costa and Solano counties, Kroll says.

All of this may change though, as several nationwide demographic trends collide. For one, millennials are having fewer children and delaying home ownership. That could change where people live in the future. Regional planners, like Kroll, are tasked with considering things like emissions and commute times when deciding where and what kinds of housing to build.

“There’s a lot of focus on density of housing. And that means more multifamily, less single-family housing,” Kroll says.

So while families may continue to move to the outskirts of the Bay Area now, things could look different in a few decades.