Most of us probably grew up with baby aspirin as a house staple. However, the American Academy of Pediatrics (AAP) now advises against giving any aspirin to children who have a fever unless specifically doctor-prescribed. Research has linked the sometimes fatal brain disease Reye's syndrome (RS) with aspirin (a salicylate compound) when it is given to a child during viral illness. Since it's hard for a parent to know the origin of a sickness, and viruses abound, it's best to avoid aspirin.
What the AAP does recommend are either acetaminophen (Tylenol) or ibuprofen (Pediaprofen, Children's Motrin), since there are few problems with short-term use. However, even these can render side effects: Acetaminophen has a kidney damage risk, so should be given only every six hours and for no more than five consecutive days, and ibuprofen commonly causes stomach upset.
Fortunately, most of the herbs recommended for adults are also helpful for children older than 6 months. Theoretically, willow bark is the exception because, like aspirin, it contains salicylates. However, there are no documented cases associating RS with willow bark.
To calculate oral herb doses for kids, divide the child's weight in pounds by 150 pounds (the average adult weight) and multiply this fraction by the adult dose on a package. Thus, for an herbal tincture with a dose of 10 drops, a 50-pound child would get 3.3 drops (50/150 = 0.33 x 10 = 3.3).
Of course, whenever a child is ill, consult with a knowledgeable health care practitioner.