Hi,
A lump behind the ear in children could be due to throat infection, insect bite, accidental trauma to the site, ear infection , etc.
Lymph nodes in the region are known as post auricular lymph nodes and can enlarge secondary to infection, inflammation, etc.
You could try some warm compresses at the site, warm saline gargles for his sore throat and some oral antihistamine medications for the swelling.
Does he have any other symptoms of fever, etc?
If the swelling still persists after a few days, it would be best to consult a doctor for a clinical examination and whether a course of antibiotics is required.
Let us know if you need any other information.
Regards.
I am 17 and growing up I had chronic ear infections and seemed to always be sick at 17 the lymph nodes behind my years are about 2 fingues wide and always swollen they have just stopped hurting as well and don't think there is anything to worry about unless they are causing them pain.