Thanks for posting the query,
sores occurs due to physical or chemical trauma .
Visit to a Pedodontist and get clinical evaluation done , look for any sharp tooth causing irritation .
Apply dologel oral ointment topically over the affected area.
Take vitamin suplements.
Maintain a good oral hygiene , clean the mouth with antiseptic solution using handkerchief or cotton this will prevent infection and promote healing .
Hope this helps out.