Thanks for the query
At this age most common cause of swelling at this site is due to lymph
node.You have not mentioned when did you notice the swelling as it may be due to some congenital causes like branchial cyst and cystic hygroma
. All these swellings are benign in nature but need evaluation. So I would suggest you to first consult a pediatrician
and if needed you may have to consult a pediatric surgeon also.
I hope this answers your query.