Hi mam.... Ulcer is break in continuity of oral epithelium.. Causes of ulcer ** vit B12 deficiency **Iron deficiency anemia ** viral infection ** stress and anxiety **irritation from sharp tooth cusps **Genetic factors  Usually ulcer heals with in 7 _10 days... Long standing ulcer is noticebale that needs immediate medical attention Ulcer in the gum region may be the gingival abscess due to infectious tooth... Clinical examination is necessary to rule out the cause... If it is identified as gingival abscess then pulpectomy of the infected teeth is indicated

Ask him to apply dologel twice a day and he will be relieved

Usually children will not get ulcers for so long. If it is on or near the gum it may be an infection related to the tooth. Even if it is a ulcer, such a long standing ulcer should be checked. Please consult a dentist or a paediatrician