A decade after the government began trying to ensure that prescription drugs used to treat children work and are safe, doctors still have scant information to guide them when they administer many medications to kids.

Although federal regulators have enticed or forced pharmaceutical companies to conduct hundreds of studies that have produced vital results about more than 200 drugs, perhaps two-thirds of the thousands of medications given to children remain untested on them.

"Are there children dying because of this? I don't know. Are there children being less effectively treated because of this? Probably yes. But I can't tell you because I don't know," said Richard L. Gorman of the American Academy of Pediatrics. "That's the problem: We don't know what we don't know."