What Causes A Discolored Patch On The Tongue With Coughing And Nasal Drip?

My 2 year old son has the symptoms of a virus which started out with a fever lasting about 2 days with coughing and runny nose and he did not have much energy nor was he eating much. My Mom had been watching him while I was having a baby we picked him up on Saturday as he seemed better but then i discovered his tongue has a discolored spot on it. I just spoke with my Mom who is now sick with the same symptoms. What could it be? Is it highly contagious? Can it be treated with antibiotics?