Two-thirds of the cases were children who took the medicines unsupervised, and most of the others were because parents gave doses that were too large, the study by the U.S. Centers for Disease Control and Prevention reported.
More than three-quarters of the cases involved kids ages 2 to 5, the CDC found.
The study included both over-the-counter and prescription medicines. It comes less than two weeks after the U.S. Food and Drug Administration warned parents that over-the-counter cough and cold medicines are too dangerous for children younger than 2.
"The main message is no medication left in the hands of a 3-year-old is safe," said the CDC's Dr. Melissa Schaefer.
CDC researchers gathered case reports of children 11 and under who had taken cough and cold medications and wound up in 63 hospitals studied in 2004 and 2005. They used that number to come up with the national estimate.
About 1,600 of the estimated 7,100 children are under 2, so the FDA's guidance - if followed - should reduce such ER cases by 23 percent.
Many of the ER case reports were not specific about symptoms, and the researchers did not follow cases through to conclusion. So they did not know if - or how many - deaths resulted, said Schaefer, an epidemiologist who was the study's lead author.
For the children whose symptoms were reported, allergic reactions like hives and itching were most common, and neurological symptoms like drowsiness and unresponsiveness were next, she said.
Most of the medicines involved were liquid combinations of cough and cold treatments, CDC researchers said.
Parents should not encourage children to take medicine by telling them it's candy, and parents should also avoid taking adult medications in front of kids, CDC officials said.
The study is focused on the misuse of medications, said Linda Suydam, president of the Consumer Healthcare Products Association, a trade group that represents manufacturers and distributors of over-the-counter medicines.
"These medicines are safe when used as directed, and this government review underscores the importance of educating consumers - especially those with small children - on the safe use and safekeeping of medicine," Suydam said, in a prepared statement.
The study was published online Monday in Pediatrics, a journal of the American Academy of Pediatrics.
