Johns Hopkins researchers, who led the study of data from 2003-2004, pointed out that 96 percent of the 821 errors never caused harm, but 4 percent did. No one was killed. But in one instance, the patient's weight in pounds was mistaken for weight in kilograms, resulting in an overdose of three different heart drugs, which sent the child into cardiac arrest, researchers said.

One thing that's missing from the study: A calculation of how often medication errors actually occur. Previous studies have estimated that 1.5 million people a year (adults and children) may be impacted.

These heart drugs are used more often in children than you might think. Four in 1,000 U.S babies are born with congenital heart disease. According to the study, most of the harmful errors involved diuretics, used to treat heart failure and lower blood pressure by ridding the body of excess water, and drugs for lowering blood pressure. Not only are these medications used in those infants but they are being given more often to older children and teens with high blood pressure.

"Medication errors are inevitable," the study says, "given the human factor in patient care."

But how can these errors be reduced? Double- and triple-checking doses, labels and safety warnings can be a start. Hospitals are encouraged to put any mechanisms in place that will reduce the chance that mistakes will happen.