I read with caution what Food and Drug Administration (FDA) of USA has issued in a public health advisory. It says parents should not give sniffling babies and toddlers over-the-counter (OTC) cough and cold medicines. The medicines can be too risky for babies and toddlers.
The warning specifically warn parents of children under age two "because serious and potentially life-threatening side effects can occur." What's of alarming is that in October 2007, the FDA's own scientific advisers voted that cold medicines targeted specifically to babies and toddlers don't even work in small babies and shouldn't be used in preschoolers, either.
We must be cautious about this serious issue. Some health groups have identified bigger risk: unintentional overdose. For example, the same decongestants, cough suppressants and antihistamines are in multiple different products, therefore using more than one product to address different symptoms can quickly add up to overdose. And in the case of having multiple caregivers with different administration of doses, overdose is a big risk.
PS: This writing comprises mainly the article from AP.