My son was 15 months old when prescribed Zyrtec three months ago. The allergist said to give between 1/4 and 1/2 of a teaspoon once a day. His weight at the time was 25 lbs. The allergist said to give between 1/4 and 1/2 of a teaspoon once a day. 2 - 6 years of age: 2.5 - 5 mg given once daily (maximum dose 5 mg daily) Over 6 years of age : 5 - 10 mg given once daily (maximum dose 10 mg daily) Zyrtec comes in a 1mg/ml solution (so 2.5 mg = 2.5 ml). My daughter has been on zyrtec since she was 6 months old. she is now a year old. she is also on singulair and two inhalers. the combination of everything has really helped her cough/allergies. I'm not sure about Zyrtec, but I have my 2-year-old and 9-month-old on Nasonex. It works for the most part. I've been giving it to my oldest since he was nine months during the Spring and Fall. You may want to switch to that. It won't give the medicine head feeling to them. Good luck!! I give the children's zyrtect to my son. Dr. said to when he had a rash which was probably from eating yellow squash for the first time. He was between 6-7 months old and about 22lbs. They said to give 1/2 tsp. once every 24 hrs. before bed. My three year old was miserable for 3 days while taking Allegra and the pharmacist recommended Zyrtec. It made her feel so much better and she is back to her old happy sweet self. So thankful I found Zyrtec for her! Can I give my 18 month old benadryl for allergies (runny nose, watery itchy eyes and sneezing) after he's already received a 1 tsp dose of cetirizine (zyrtec) approx 5 hours ago? If so how much? He's My oldest child/daughter was on zyrtec about some where between 6-9 months. Her doctor told me she had allergies and wrote a prescrition for her out. I would talk to a their doctor first. :) Her doctor told me she had allergies and wrote a prescrition for her out. My son has allergies and he is 6 months old. His eyes get really red and puffy and he coughs a lot. My doctor gave us Zyrtec for it. I give him 1/2 teaspoon a day and it seems to help a lot. his cough is completely gone and he only gets red eyes if he gets near our cat. When it comes to giving your child Zyrtec, you need to make sure you are giving him or her the correct dosage. Giving your child too little medicine will not help them with their allergies, but giving them too much medicine can result in an overdose.