Hi.
Sorry to hear about the kid. Swelling below the ear might be due to
lymph node or it may be a parotid swelling like
mumps.
Here are few words that may help you .
If we take it to be a lymph node then we need to see the areas that drain lymph to these group of lymph nodes. So look for any boil,
skin infection on that side of
scalp, and dental problem or any signs of
otitis ( both external and internal) any type of boil on ear or any discharge from ear. Seeing your description , history of having pain in ear on that side suggest some thing is wrong with ears/throat and all you need is to visit an ENT doctor to get further help/advice.
IF we take up the next option (mumps) , then look for any
rash on the face and body. Although in this era of
vaccination , mumps is less likely but still it exists. In that case you may need to visit a doctor with qualifications in infectious diseases/ internal medicine. Wishing your kid a best of health forever. If you have anymore questions, i would be pleased to help you with the best of my knowledge and experience. Regards.