For several decades now, San Francisco has had one of the lowest percentages of school-age children and teens of any major city in the country. And the latest numbers from the 2020 Census show that SF's youth population has only decreased as a share of the total population in the last ten years.

We learned on Thursday, with the release of data for the purposes of congressional redistricting, that SF's population rose by about 90,000 people between 2010 and 2020. And while California and the country as a whole grew increasingly diverse, San Francisco's demographics shifted only slightly in the last decade, with the percentage of white people declining 2.8%, the percentage of mixed race people rising from 3% to 5%, and other demographic percentages moving less than one percentage point up or down.

Now, according to a Chronicle analysis, we learn that San Francisco's percentage of children under the age of 18 slipped from 13.4% in 2010 to just 13% in 2020 — a continuation of a trend that goes back to 1990 when youths represented 16% of the city's population.

Growing up in San Francisco continues to be an uncommon thing, largely driven by a lack of affordable family housing, and various other factors including a less than stellar public school district.

Much of the Bay Area has lower percentages of kids under 18 than other parts of the country, but San Francisco has the lowest share by far — the next in line is Sonoma, with nearly 20% of its population under 18, and Contra Costa County has the largest share, with 22.6%.

What does this mean for the city overall? Unfortunately it could mean continued lack of broad support for the school system, though an investment in the city's schools could succeed in keeping families with small kids from fleeing the city when those kids reach school age.

Former Supervisor Norman Yee, as the Chronicle notes, wrote a policy briefing four years ago arguing for the creation of more affordable family housing, saying, "When we lose our families, we lose part of what makes San Francisco a strong, vibrant community."

And former director of the Planning Department John Rahaim wrote in an introduction to the paper, "We have a responsibility to implement family friendly housing policies that will allow families from all socioeconomic backgrounds to live here and thrive."

But how do you reverse a trend that's been ongoing for 30 years, coupled with an era when fewer people are having kids overall? The short answer: you probably can't. But maybe they can keep the percentage of kids from falling any further.

Related: Census Data Release Shows US and California Growing More Diverse — and San Francisco Gained 90,000 People

Photo: Jairo Gonzalez