Hi, thanks for writing to us! In the present case of recurrent lump on the back of head of your son, if I were your consulting physician, I would also just say you, nothing to worry! As per your description, it disappeared some times back and now it re-appeared; therefore it is simply an enlarged lymph node due to infection in local regions like scalp, ear, throat, neck etc...! However, sometimes it could be converted into an abscess or may harbor tuberculosis and needs treatment... Take caution not to get him injured there as this might invite infection. Please do an FNAC test for confirmation and plan line of treatment if needed at all! Hope you got your answer. Please feel free to write to us if any more queries. Wishing your son good health!