Hello, I had gone through your question I can understand your concern about the halitosis of your son. As you said he gets air via mouth is one of the important reason for bad breath (halitosis). As he takes a it through mouth there is dryness of mouth which intern provides better environment for mouth bacteria to ferment what ever Carbo hydrates ans other food stuff is found in mouth that leads to bad breath. There are many reasons of mouth breathing like mal occlusion of teeth, tonsillitis, over weight, faulty sleep habits and many mere you need to get checked by an pediatric surgeon as well as dentist the proper cause. During mean time use flavored tooth paste twice daily, Saline gargle before sleep, avoid upward or downward sleep. Use local antifungal gel like CANDID if his tongue is white coated. Hope my answer will help you. Regards Dr Muzaffar Yo