i can't offer you a definitive answer based solely on your brief description. i would need to see and exam this child but one possibility would be impetigo -- a staph or skin strep infection. there can certainly be many other causes. ten year olds like to swing on bars during recess and often get blisters. if they pick at those blisters on a dirty hand it can become secondarily infected and this infection can spread to the mouth quite easily.
my 10 year old got a hand blister and now she has scabs around her mouth. what could this be. the blister had skin coming out. the mouth stores just happens when she woke up from a nap