My 8 month child has several swollen lymph nodes behind both ears. What can cause them?

Infections. The lymph nodes behind the ears and on the back of the neck are part of the huge system of infection-fighting 'lymph'. Each group of nodes (lumps) relates to specific areas of the body, so swelling behind the ears could be related to ear infection, scalp infection or irritation, and upper respiratory infections. Even after the infection is cleared, the lumps can remain for days to weeks.