Researchers at the Rand Corp. found despite having paid into the program through payroll withholdings, the vast majority of these parents were not aware that the program exists --18 percent were aware of the program and 5 percent had used the benefits.

Adopted in 2004, the California program is the nation's first paid family leave law funded by employees through an automatic payroll deduction -- averaging about $1 a week -- that goes into a state insurance pool.

After a one-week waiting period, the program annually provides most employees six weeks of non-job-protected paid leave paying up to 55 percent of an individual's salary to care for ill family members.

The study, published in the Journal of the American Medical Association, said about 18 months after the program began there was no significant change in the numbers of parents taking days off.

Parents of chronically ill children remained at work because they feared losing income, losing their jobs and damaging their careers, the researchers suggest.