Aug 28, 2013 (MOTRIN, ADVIL, PEDIACARE FEVER) When Should Ibuprofen be Although the package might not give a dosage for under two years, it can be safely used down to two If it wears-off too soon, then use a dose of Acetaminophen. 1 tsp (5ml) of children;s liquid and ½ tsp (2.5 ml) of infant...