"It can take just a few seconds for children to grab them, break them open, and swallow the toxic chemicals they contain, or get the chemicals in their eyes."

Nearly half of children vomited after laundry detergent pod exposure, the researchers said. Other common effects were coughing or choking, eye pain or irritation, drowsiness or lethargy and red eye or conjunctivitis.

A leading manufacturer of laundry detergent pods began changing its packaging in the spring of 2013, introducing containers that were not see-through and adding latches and a warning label to the containers, the researchers said.

However, laundry detergent pods from many makers continue to be sold in see-through packages with zip-tops or other easily opened containers, they noted.

"It is not clear that any laundry detergent pods currently available are truly child resistant; a national safety standard is needed to make sure that all pod makers adopt safer packaging and labeling," said lead author Gary Smith, director of the Center for Injury Research and Policy at Nationwide Children's Hospital.

"Parents of young children should use traditional detergent instead of detergent pods."

The study was published in the U.S. journal Pediatrics.