The most important fact that you mentioned about your grandson is that he does not face any serious discomfort or pain at all. In all likelihood, there is really nothing that you need to worry about as the condition is sometimes quite normal. Your concern that the feeding equipment is not completely sterile might definitely be a cause for concern. Ensure that the feeding equipment is completely sterilized in boiling water before every feeding session to ensure that the baby is not overwhelmed with bacteria at such an early age.
Some of the possible reasons for the appearance of a white spot would include bacterial infections, fungal infections, and a white sponge nevus. These are not necessarily infections that occur in children only. Bacterial infections in small children are quite possible because they usually end up putting everything they can get their hands on in their mouths. Should the tongue have gotten a minor cut in the process, this would then cause the development of a boil. It is also worth noting that the formulation given to the child during feeding might have been too hot for the delicate skin of the tongue. This will then cause a minor rash and the appearance of a boil. Fungal infections are also a possibility but this doesn’t really manifest in the form of a boil. Rather, it looks like a formation of mushrooms at the very back of the mouth or as a white film. This condition should not be taken lightly and the child must be immediately taken to the doctor for the proper antifungal medication. This can be eliminated as a possibility since the spot is on the child’s tongue. The last possibility is that your grandson has a sort of a keratosis happening on the tongue. Keratosis is usually a skin problem though it can happen inside the body as well – where it actually shouldn’t.
This is a condition called white sponge nevus and is caused by a mutation in the keratin producing genes. The condition can sometimes be confused with other plaque causing conditions but you needn’t worry about a misdiagnosis because the condition is benign and will go away on its own without any intervention required. This is the most likely cause since your child is not experiencing any other kind of symptoms like fever, pain, or other signs of infection. To be completely sure, consult with your doctor as well.