Here's a NYTimes article on the possibility of children's cold medication causing more harm than good. The consensus of the FDA expert panel boils down to the fact "that if the drugs had not proven to be effective in young children, they should not be available." It seems that in the '70s regulators decided what works for adults should also work for children (using different doses of course). Since then though, many studies have shown the efficacy of these OTC cold drugs to be debatable and in the worst cases, causing serious harm.
Its shocking to me that medication like Robitussin, which I was given routinely for a cough when I was young, could have had an adverse effect. The numbers explain a lot: "Parents spend around $500 million every year buying nearly 95 million boxes containing 3.8 billion doses of medicine." Hence the manufacturer uproar against the possible ban on OTC drugs for children below the age of 6. Lobbying power makes all the difference in health care (and most other sectors as well).
The director of the FDA office of new drugs advises parents to be more careful reading labels, which while smart practice in general, is difficult to expect of parents who most likely aren't versed in medical terms and are worried sick about their children's condition. The gap in medical education is primarily the reason expert FDA panels have to be convened to pass such bans on drugs. Maybe pharmacists should start getting more involved.