Hi. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns... As per your complain it seems that your son is suffering from viral infection that can be due to herpes virus causing herpetic gingivostomatitis and can lead to fever, swollen gums and in a day or two there can be outbreaks of blisters in and around the mouth known as cold sores.. In case if there are erupting blisters in other parts of mouth too then it can be due to Hand foot and mouth disease that is again a viral infection caused by ENTEROVIRUS.. Consult a Paediatrician and get him evaluated and he can do a clinical evaluation and blood tests to confirm the diagnosis.. As of now you should feed your son with a soft ,cold and bland diet, a low spice vegetable soup, flavoured gelatin, bread socked in milk etc can be given.. Avoid citrus juices like orange juice and can give him fresh apple juice.. For fever you can give him Tylenol or Acetaminophen .. Application of a numbing gel like Lignocaine over the gums and other sore areas of mouth can provide relief, but care should be taken not to involve large areas of mouth as when being numb the child can accidentally bite the tongue and also damage other areas of mouth unknowingly.. Sucking ice pops or a frozen apple juice popscicle can help in reducing inflammation and discomfort... Maintain a good oral hygiene and use an ultra soft toothbrush for brushing can help by preventing trauma and pain to gums.. Hope this information helps.. Thanks and regards.. Dr.Honey Nandwani Arora..