We examined the effects of health insurance on access and utilization of health care among children of working poor families. These children experience strong access barriers yet have not been studied systematically. 1,492 children in California under 19 years old who had workforce participating parents and a subset of full-time year round working families earning below 200% of poverty were examined from the 1994 National Health Interview Survey. Thirty-two percent of children of working poor families were uninsured in California compared with 26% nationwide. Difficulties in accessing a regular care source and obtaining after-hour care were markedly higher in California. Full-time year round work did not increase insurance coverage and worsened access to a regular source of care. Uninsured children in California were far more likely than insured children to face access barriers and less likely to see a physician in the previous year. Between privately and publicly insured children, the gap in access and utilization narrowed markedly. Health insurance is critical for children in working poor families. Healthy Families, California's response to CHIP, could improve coverage for this population.