In version 10.0 HP had not yet split the ALL_LISTS table into two. So the query for your version would be:
SELECT AL_DESCRIPTION FROM ALL_LISTS WHERE AL_FATHER_ID = (SELECT AL_ITEM_ID FROM ALL_LISTS WHERE AL_DESCRIPTION = 'Severity')
SELECT AL_DESCRIPTION FROM ALL_LISTS WHERE AL_FATHER_ID = (SELECT AL_ITEM_ID FROM ALL_LISTS WHERE AL_DESCRIPTION = 'Severity')