When it comes to taking medicines, kids aren't just small adults. For prescription medicines, there is a "Pediatric" section of the label. It says whether the medication has been studied for its effects on children. It also tells you what ages have been studied. Aside from drugs for fever or pain, most over-the-counter products haven't actually been studied in children for effectiveness, safety, or dosing.
When you give medicine to your child, be sure you're giving the right medicine and the right amount. Read and follow the label directions. Use the correct dosing device. If the label says two teaspoons and you're using a dosing cup with ounces only, don't guess. Get the proper measuring device. Don't substitute another item, such as a kitchen spoon. Talk to your doctor, pharmacist, or other health care provider before giving two medicines at the same time. That way, you can avoid a possible overdose or an unwanted interaction. Follow age and weight limit recommendations. If the label says don't give to children under a certain age or weight, don't do it.
Food and Drug Administration
References and abstracts from MEDLINE/PubMed (National Library of Medicine)