He could have Lupus.... read about Lupus online... can happen to anyone at any age.
take him in asap he should be seen if infection of a lymph in that area can lead to unseen problems especially with swelling
You should take your son to the doctor to get his ear checked out. Although the lymph node is swollen he may have an infection and blockage in the ear and eustation tube.
This may be a viral or bacterial infection and your doctor will be able to prescribe an antibiotic if this is a bacterial infection. The doctor may prescribe an ear spray if his ear is swollen and also a nasal spray to help with the internal congestion.
Keep him comfortable and give him lots of drinks (not fizzy or milky) to make sure that he does not dehydrate. For the pain give him pain relief in the recommended dosage for his age.
You can place a bowl of hot water with Vick or olbas oil to get more moisture to the room to help with congestion.
If his neck starts to swell just below the ears, this may be mumps, which is a virus and needs to run its course. If that is the case keep him warm and out of any draughts.
Make an appointment for him to see the doctor.
Best wishes.