Children who grow up in the Bay Area—particularly in Marin County—are more likely to live in affluent households, be enrolled in preschool, have health insurance and score better on standardized school tests than kids living in rural areas of California, according to a study to be released today by Children Now, a statewide advocacy group.

The findings, based on census and state health and education data, didn’t surprise Children Now senior policy associate Corey Newhouse.

“Income trumps everything,” Newhouse said. “In low-income rural counties, it’s a double whammy. Families in general don’t have the kinds of financial resources to access what they want for their kids, and the services tend to be spread out.”

The study found that families in Marin County, where the median family income is about $112,200 a year, had the most economic well-being, followed by San Mateo, Placer and Contra Costa counties. Families in Del Norte, Lassen, Modoc and Siskiyou counties, where the median family income is about $30,400, had the lowest economic well-being.

In Marin, 96 percent of mothers received early prenatal care—the highest percentage of the state’s 58 counties. The lowest percentage is in Merced, where 64 percent of mothers received prenatal care. The median family income there is about $42,700 a year.

Seventy-four percent of Marin’s 3- and 4-year-olds are enrolled in preschool, compared with a low of 23 percent in Tulare County, where the median family income is about $35,600 a year.

The report shows that children do well in the rest of the Bay Area.

San Francisco has the state’s highest percentage of insured children—100 percent—thanks to a city-sponsored program. San Francisco had the second-highest percentage of high school graduates who meet University of California and California State University entrance requirements—54 percent.

Children Now’s Newhouse said she’s concerned about the low percentage of children across the state attending preschool. On average, 42 percent of the state’s 3- and 4- year-olds go to preschool.

“We are concerned that so few counties have crossed the 50 percent threshold,” she said.

Children Now, which compiles this data every two years, hopes the information gets into the hands of state policymakers, who can help make children’s lives better.