What causes little bumps behind a childs ear

Lymph node swelling: Our immune system includes a number of way stations where immune cells (lymphocytes and others) congregate and fight infection. These are called lymph nodes. The ones located behind the ears ("posterior auricular") can enlarge during a viral infection, or from inflammation involving the outer ear or scalp, as in swimmer's ear or seborrhea of the scalp. Malignancy would be a rare cause.