The dosing instructions for children taking Benadryl are based on the child's weight; for example, a child weighing 25 to 37 pounds should take 1 teaspoon of Benadryl, one 12.5-milligram Benadryl chewable tablet or one 25-milligram capsule, according to St. Louis Children's Hospital. Regardless of the dosage size, the dose should be repeated every 6 hours as needed or as directed by a physician. The dosing guidelines for Benadryl are published on the St. Louis Children's Hospital website and are current recommendations as of 2015.
Larger children are given larger doses. For example, a child weighing 50 to 99 pounds should take 2 teaspoons of Benadryl liquid or two chewable 12.5-milligram Benadryl tablets. Children over 100 pounds should not be given Benadryl liquid in most instances, but instead should take the chewable, tablet or capsule forms of the drug.
When used for allergies, children under age 1 should not be given Benadryl, and Benadryl should not be given to children for treatment of colds at any age, so there are no proven benefits to using it for this purpose. Unless directed by a doctor, Benadryl should not be given to any child under age 4, and children under age 5 shouldn't be given products that contain Benadryl along with additional ingredients, warns the St. Louis Children's Hospital.