In 2007, amid mounting concern that infant cough and cold medicines were unsafe and misused, manufacturers voluntarily withdrew products intended for children younger than 2. The makers revised the labels on the rest of the medicines, which now warn parents that they should not be given to children younger than 4.

Government researchers said Monday that those moves have had a remarkable effect: a significant decrease in emergency hospital visits by toddlers and infants with suspected medical problems after using these medicines.

Dr. Daniel Frattarelli, a former chairman of the committee on drugs at the American Academy of Pediatrics, praised the study, saying it showed that “the label is a very powerful tool for changing parent behavior.”

In the new study, published in the journal Pediatrics, researchers at the Centers for Disease Control and Prevention reviewed data from 63 hospitals to estimate the number of emergency visits from 2004 to 2011 by young children who had taken cough and cold medicines.

Children younger than 2 accounted for 4.1 percent of all emergency visits for suspected drug-related effects before the 2007 withdrawal, the researchers found, and accounted for 2.4 percent afterward. Among 2- to 3-year-olds, emergency-room visits linked to cough and cold medicines decreased to 6.5 percent from 9.5 percent after the label change.

Yet there was no significant reduction in emergency visits among children ages 4 to 11. Among 4- and 5-year-olds specifically, visits attributed to cough and cold drugs increased to 6.5 percent from 5.6 percent.

“We’re making great progress in under-2s, and we’re making relatively good progress in 2 to 3s,” said Dr. Don Shifrin, a pediatrician in Seattle and a spokesman for the American Academy of Pediatrics. “But we’d like better news for kids over 4.”

The new report may reignite the debate over when it is safe for parents to give cough and cold medicines to their children, some experts said.

Frattarelli said he would like to see “do not use” labeling for children ages 6 and younger, since the drugs continue to be misused for 4- and 5-year-olds.

“The label doesn’t reflect the current evidence that these medications are ineffective for treating cough and cold symptoms in kids under 6,” he said.

The new report also found that most babies and toddlers who turned up in the emergency room for problems thought to be related to these medicines managed to get their hands on them when a parent’s back was turned.

“Of adverse events still occurring, 90 percent in 2- to 3-year-olds were unsupervised ingestions,” said Dr. Daniel S. Budnitz, senior author of the paper and a medical officer in the CDC’s Division of Healthcare Quality Promotion.

“Two-year-olds don’t look at labels; they just look at colors,” Shifrin said, adding that curious youngsters jump at the chance “to sample medicine that looks and tastes like candy.”

Dr. Tricia Jean Gold, a pediatrician in Brooklyn, said she had a 3-year-old patient who recently drank cough medicine that her 10-year-old sister had left on a bathroom shelf with the cap secure. The toddler experienced an elevated heart rate, became agitated and then drowsy, showed signs of an overdose and ended up in an emergency department, she said.

In a national poll last year, two-thirds of adults supported requiring medicines to be packaged as single doses.

Though Gold understands why parents turn to cough and cold drugs, she said she found it “astonishing” that emergency-room resources were still squandered on “products that are not proven to work and have been repeatedly implicated in adverse events.”

Still, this year, four in 10 parents reported giving cough medicine or multisymptom cough and cold medicine to children younger than 4, according to a C.S. Mott Children’s Hospital National Poll on Children’s Health in January.

Dr. Jennifer Shu, a pediatrician in Atlanta, said, “There’s a new batch of parents who seem to be oblivious.”