Millions of young children spend about 35 hours a week in child care while their parents work. But a new study shows 26 states received a failing grade for child care center regulation and oversight.

The National Association of Child Care Resource and Referral Agencies gave no one an A grade. Only one entity the equivalent of a B grade for its child care programs -- the Department of Defense. 

Though child care programs receive about $10 billion a year from taxpayers, three states and the District of Columbia received a C grade. Twenty-one remaining states earned a D in the report. 

Most states have serious gaps in how they regulate those centers, according to NACCRRA, a nonprofit group that coordinates with 700 local and state child care agencies. Some states don't require comprehensive background checks for workers, some don't check new hires against child abuse reporting records and many do not require child care teachers to have a high school degree. 

The problems ranged from gaps in licensing to gaps in background checks. One state, South Dakota, does not require operators to obtain a license until 13 kids are being taken care of in a home, according to the report. The report found only 10 states require comprehensive background checks, while seven states do not require child care centers to look up potential hires on the child abuse registry. 

"The reality is that most state licensing requirements are weak and oversight is weaker," the organization's director, Linda Smith, said in a written statement. "The safety of a child in child care should not depend upon the state in which the child lives." 

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Aside from the Department of Defense, the top four on the list were Oklahoma, the District of Columbia, Illinois and Massachusetts. 

NACCRRA praised the Department of Defense for having strict licensing standards, requiring inspections of child care centers at least four times a year, and requiring comprehensive training for workers. 

At the bottom of the list were Idaho, Louisiana and California. Louisiana is one of the states that does not require workers' names to be checked against the child abuse registry. 

Texas, where a recent deadly fire at a daycare center made national headlines, tied for 16th place with Michigan. 

The report, though, said states have made progress by increasing inspections, increasing teacher requirements and doing a better job meeting health and safety standards. 

The organization recommended that all states require comprehensive background checks, require at least 40 hours of initial training for workers and require inspection results to be posted online. It also recommended that the federal government withhold funding from states that fail to meet minimum standards.