Hello, I can understand your concern. The most common cause of green tongue in babies is presence of fungal/yeast infection on the tongue. It would have been helpful if you had mentioned what medicines are being given to him and if it includes antifungal medications. Sometimes, use of antibiotics can also cause development of fungal growth on tongue. Other causes may include presence of bacterial infection causing hairy tongue and possible upper respiratory tract infection. I would advise you to go for analysis of tongue swab in the laboratory. It can be done with the help of a dentist. Based on the analysis result, confirmed diagnosis can be reached and treatment can be started. I hope this information helps you. Thank you for choosing HealthcareMagic. Let me know if you have follow up questions. Best, Dr. Viraj Shah