It might be an allergic reaction or a bee sting in the mouth, they may also have gingivitis - a very severe case. I suggest going to that medical md site and checking it out or go to a pediatrician, Or they might have just eaten something they should not have eaten, household plants, animals, anything like that...think outside the box since they are a 2 year old child. Hope I helped - good luck hope they get better!!! Byebye