I can tell you that my three year old gets 5ml for allergic reactions and seasonal allergies.and has been on that dose since she was 2 years old. She is around 50% percentile for weight. She is around 50% percentile for weight. Doctors give trusted answers on uses, effects, side-effects, and cautions: Dr. Hegab on benadryl dosage for 2 year old: Topical Benedryl is considered safe to use in toddlers. It is not recommended if the child is also taking oral Benedryl at the same time. Doctors give trusted answers on uses, effects, side-effects, and cautions: Dr. Hegab on benadryl dosage for 2 year old: Topical Benedryl. Dear mechelle, The symptoms of allergy are usually controlled by one to two doses of benadry.You may give her initially 25 mg and if the symptoms are not controlled then repeat the dose after a few hrs.The benadryl is safe drug but excess should be avoided. Children - BJC HealthCare My grandson's pediatrician prescribed 12.5ml of Benadryl for a rash that has now. The dose for a 12-year-old is 20ml(cc) up to every 4 hours if needed. we had to give some to our daughter because she had a sinus infection and we were flying home in two days. They told us that it would help the swelling in her sinus cavity and ear canals. Who knew? Anyway the pharmacist told us the correct dosage, if you pick some up stop my the pharmacy counter and they can help. I have to give my 2 year old daughter Benadryl for allergies pretty often. The dose for her is 1 teaspoon and she weighs 29 pounds. Hope that helps. The dose for her is 1 teaspoon and she weighs 29 pounds. I gave my 9 year old Zyrtec this morning and with the change of temp and cold weather his allergies are really acting up, so I gave him 12.5 mg of Benadryl tonight along with his singulair. I wanted t … Give your children effective relief from allergies with a liquid allergy medicine that’s cherry-flavored and contains an antihistamine that helps them feel better when they need it. 1 teaspoon or 5mL of children's benadryl active ingredient diphenhydramine 12.5mg A very conservative dose would be 2.5mL. My son began taking the 5mL at 18 months old per doctors orders, however he is larger than most, at two he weighed 30 lbs and is 36 now at 2.5yrs.