Nebulization has NO role in cold,it's used only for problem in the lungs,e.g asthma. Give only steam inhalations 4-5 times a day,and paracetamol for fever and repeat every 4 hours if required. If not improving OR accompanied by other symptoms like vomiting or loose motions or coughing and breathlessness or dullness,consult your paediatrician asap.