Seattle ? Nearly one-third of paid child care workers are relatives who often lack training and government oversight, according to a national study released today.

About 2.3 million people a larger number than previously thought earn their money by caring for preschoolers, the study commissioned by the Department of Health and Human Services found.

The study involved 7,000 households and focused on people who care for children up to age 5. It was performed by researchers at the University of Washington and the Center for the Child Care Workforce.

“This is a very critical development phase. They soak up learning like sponges,” said co-author Richard Brandon, a senior researcher at the university. “We need people appropriately trained to teach them.”

The Census Bureau has estimated the size of the child-care work force at 1.7 million. But the study was the first to include paid grandparents and other relatives who care for many of the nation’s children.

Economist Jared Bernstein, former deputy chief economist at the Department of Labor, noted that the study provides an update on child care at a time when more parents are working.

“Over the past decade, the demand for child care has increased. The study has an urgency now that it didn’t have 10 years ago,” Bernstein said. “Who’s minding the kids is crucial.”

Brandon said the study illuminates the need for more training and support, especially for informal and unlicensed caregivers. According to the Labor Department, child care is one of the nation’s fastest-growing occupations.

“You want to find the isolated, clueless caregivers and give them help,” Brandon said.

Advocates for child care workers said they hope the study will make politicians and the public appreciate the number and importance of child care workers.

“They do have a large impact on our future,” said Faith Wohl, president of New York-based Child Care Action Campaign.