“The bottom line,” he said, “is that for all of the over-the-counter cough and cold medications, there is limited to no evidence of efficacy for any cold symptoms, particularly in those under 6 years.”

Studies have not shown that cough suppressants help children cough less, or that antihistamines and decongestants help them sleep better. Medicines which can help a child with a runny nose from seasonal allergies won’t help that same child when it’s a cold virus making the nose drip; the underlying mechanisms are different.

Even for older children and adolescents, Dr. Paul said, the evidence of efficacy is not strong for most of the ingredients in cough and cold medications, and there is always the danger of side effects, particularly when the medicines are taken in too-large doses, which can happen because there are so many different preparations, with so many different combinations of drugs.

Dr. Yin is working on a project funded by the F.D.A. to improve the labeling and dosing instructions on children’s cough and cold medications; so far, she said, the research has shown that parents in the study population are confused about the intended age ranges of the medicines, about the active ingredients, and about dosing. Many of these preparations contain several different drugs, including a cough suppressant, a decongestant, an antihistamine and a medicine for pain and fever.

“In my own practice, I reassure them, I check the child, I make sure I’ve covered the ears, the lungs, the throat,” Dr. van Driel said. “I reassure the parent, this is a cold, a cold is a self-limiting disease, we have capable immune systems that will take care of it, it will take about a week.” People need to feel confident in their bodies, she said, instead of relying on medicines. “I would tell them, there’s not a lot we know that helps. Don’t give him anything you might give your older child or take yourself,” said Dr. van Driel.

And of course, we always tell parents what to watch out for, symptoms that might suggest that something more than a cold is going on. Any respiratory difficulty in a child has to be taken seriously, so a baby who is breathing too fast or a child who is working harder than normal to breathe should be checked out. High fevers are concerning, as are any of the signs of influenza, such as shaking, chills and body aches; influenza in children can be treated with antiviral drugs — and prevented with flu shots.