Thank you for your query.
I hope there is no reason to worry. It might be a case of gingivitis
or a cyst in the gums.if it was associated with recent tooth eruption
then it might be normal.I hope there is no history of trauma to the gums.Apply some local antibiotics to that area.Maintain a good oral hygiene
with medicated mouthwash.If the swelling persists then consult a pediatric dentist
if possible.Hope this answers your query.have a nice day.