There is no fastest way to treat a 3 year old baby’s runny nose.A 3 year old baby’s runny nose may be related to respiratory infections, allergic rhinitis, allergies, etc. It is recommended to get rid of the allergens, and to give anti-histamine and anti-infective medications. 1. Respiratory tract infections: mostly caused by viruses, generally do not need special treatment with antiviral drugs. If combined with bacterial infections, antibacterial drugs such as cefixime and amoxicillin should be used; if caused by influenza virus, antiviral drugs such as oseltamivir can be used. 2. Allergic rhinitis: pediatric allergic rhinitis is considered to be related to environmental and genetic factors. It may cause nasal itching, nasal congestion, watery nasal discharge, sneezing and other symptoms. Antihistamines such as cetirizine hydrochloride can be given to improve symptoms such as itchy nose and runny nose. 3. Allergy: If you are allergic to allergens, contact with allergens or inhaling irritating gas or cold air may cause runny nose. It is recommended to find and get rid of allergens, which can help improve the symptoms. If your baby sneezes and runs a clear nose frequently, it is recommended to consult the pediatric internal medicine department of the hospital. The above medications need to be used under doctor’s supervision.