Children's Nyquil is part of the Antihistamine / Non-narcotic Antitussive Combinations class and treats Cold Symptoms and Cough. Antihistamine / non-narcotic antitussive combinations are used to treat cold symptoms, allergic rhinitis, cough, and nasal congestion. They work by suppressing cough and blocking the action of histamine which causes allergic symptoms. Children's Nyquil is only available as a brand name drug.