Thank you for your query on Healthcare Magic.
The swelling may be due to a lymph
node which usually present in that area.
As there is no other associated symptoms, nothing to worry.
Just observe for any change in size, color, appearance of pain.
If you find any skin infection
in the scalp
it may be related to this swelling as the lymph nodes will enlarge due to infection in its draining area.
If there is any bacterial skin infection in the scalp it should be treated with antibiotic cream application.
If find any change in the swelling , consult again your pediatrician
for re examination.
Hope I have answered your query.