The estimate comes from an analysis of 30 years of national data, and it bolsters other recent evidence on the pervasiveness of youngsters at economic risk. It suggests that almost everyone knows a family who has received food stamps, or will in the future, said lead author Mark Rank, a sociologist at Washington University in St. Louis.

"Your neighbor may be using some of these programs but it's not the kind of thing people want to talk about," Rank said.

The analysis was released yesterday in the November issue of Archives of Pediatrics and Adolescent Medicine. The authors say it's a medical issue pediatricians need to be aware of because children on food stamps are at risk for malnutrition and other ills linked with poverty.

Food stamps are a Department of Agriculture program for low-income individuals and families, covering most foods although not prepared hot foods or alcohol. For a family of four to be eligible, their annual take-home pay can't exceed about $22,000.

According to a USDA report released last month, 28.4 million Americans received food stamps in an average month in 2008, and about half were younger than age 18. The average monthly benefit per household totaled $222.