How did your sons ear get swollen? Hit with something? A bee sting? Slept on it funny? If he seems to be ok, not drowsy, not in pain, no loss of vision or balance, and you know the cause of the swelling is not something serious, I would let it heel itself. You may help it with a cool cloth to reduce the blood flow and that should bring the swelling down, but otherwise it should be ok. If there are signs of trauma or if the cause is unknow it may be wise to visit or call his doctor.
where is it swollen the outside part or the inside. my kids used to get ear infections all of the time (4 boys with ear infection AGH) any way sometimes they would cry like bloody murder and other times they wouldn't cry and I would have to go in for a chek up and they would have an ear infection and need medication. I would call his doctor and just check with them
it could be a bug bite or a bee sting.
good luck
michelle