Hello. a small bump barely measuring a centimeter which has never caused any symptoms could possibly be a lymph node swelling. It is important to ensure there are no other swellings anywhere in the body like underneath the chin, angle of jaw and neck region. An isolated swelling behind the ear in an otherwise playful healthy child is not an immediate cause of concern. If however it continues to increase in size, become painful or warm to touch, a fine needle introduced into the lump to aspirate the contents can help in diagnosis. It is known as FNAC and at the same time a CBC can be done to rule out infection.