WASHINGTON - Hoping to halt the growing number of injuries to infants and toddlers, the F.D.A. issued an advisory warning to parents never to give cough and cold medicines to children under the age of 2 unless instructed to do so by a doctor.

The warning is part of a broad reassessment by the agency of the safety of the popular medicines, which have been blamed for hundreds of adverse reactions and a handful of deaths in children under the age of 2. Registered Nurses have been advocating stronger warnings and prohibitions for years. The F.D.A. will convene a panel of independent experts on October 18th to discuss whether more warnings are required. Such meetings often signal that the agency is seriously concerned about the safety of the drugs under review.

The drugs? labels currently advise parents to see a doctor before giving the medicines if their child is under the age of 2, but too many parents are failing to heed this advice, the agency said.

?We continue to see adverse effects associated with the medicines because people are not using them properly,? said an F.D.A. spokeswoman.

If parents continue to use the drugs inappropriately for young children, the agency could take more serious action, like restricting the drugs? wide availability. Most drugs that have been taken off the market in the past twenty years were because FDA warnings went unheeded by both physicians and patients.

Some prominent registered nurses and nurse pediatricians said that the drug agency?s advisory did not go far enough.

One group petitioned the agency to ban the marketing of the drugs for children under the age of 6, and some said that these medicines should no longer be sold over-the-counter at all.

But the drug makers say that the F.D.A. approved the drugs because they are safe and effective. A spokesperson for the Consumer Healthcare Products Association, said that "the drugs labels already advise against their use in children under the age of 2 unless a doctor approved", commenting further that "there is no need to raise this age limit to 6."

Some of the drugs have drawings or pictures of infants in diapers on their labels.

The debate results because the standards for drug approvals have changed sharply in the decades since many of the medicines in children's cough and cold products were approved. If those drugs were currently up for review, they would not be approved for use in children because the manufacturers never tested them thoroughly in children.

Instead, the drug makers performed studies in adults and then simply assumed that they would work in children. Such assumptions, once common, are no longer acceptable. Indeed, a growing number of studies in children suggest that cough and cold medicines work no better than placebos.

Among the ingredients that have caused concern are anti-cough medicines including dextromethorphan, which is the DM in many preparations. They can cause neurological problems, including abnormal movements and hallucinations, even in standard doses.

Another is pseudoephedrine, which is a decongestant that has been associated with infant deaths, increased blood pressure and arrhythmias.

Some of the injuries and deaths associated with these products have resulted when parents gave two different products to their child, not realizing that both contained identical medicines, resulting in an overdose.

In rare cases, children have been injured when given recommended doses.

Everyone agrees that more studies in children are needed, but companies have little incentive to undertake new trials because the medicines? patents long ago expired. So the F.D.A. must decide how to regulate drugs that it knows very little about ? a now frequent situation for the F.D.A. In such circumstances, it often turns to advisory boards.

Despite the growing worries, sales of the drugs are booming. Most major pharmacies carry a dozen or more brands. The medicines are popular largely because children have an average of 6 to 10 coughs or colds every year, far more than adults.

Even many of the registered nurses we spoke to agreed that it was unlikely that the F.D.A would raise the age limit on the drugs, or that any dramatic regulatory action against the drugs was likely.