Hi Dear, Welcome to HCM Understanding your concern. As describe by you that persistent congestion along with foaming at mouth of a child .Well there can be many reasons for symptoms you mention in query like sore throat , post nasal drip , sinusitis , granular pharyngitis and acid reflux . The can be chest infection also . I would suggest you to keep your head elevated while sleeping , avoid eating spicy and heavy food , reduce intake of dairy products and avoid smoking . Consult pediatrician for proper examination . Doctor may order test like swab test , viral culture test , CT scan and physical examination with laryngoscope . Doctor may prescribe antibacterial or anti viral depending upon the diagnosis along with decongestants , diphenhydramine and expectorants . Hope your concern has been resolved. Best Wishes, Dr. Harry Maheshwari