However swollen lymphnodes behind the ears could be due to chest
infection, tonsillitis or pharyngitis, dandruff, or
infection of ear. So check and see if there is dandruff or rash or if the baby has ear infection.
Watch the lump. Do not touch everyday but once in 10-15 days. If the lump increases in size, becomes painful, changes color, bleeds, changes shape or consistency or more similar lumps appear then consult a doctor.
Hope this helps.