The widow of any county probation officer, who shall die from any cause while in the service, whether such county probation officer shall have served as such for a continuous period of twenty years or not, or whether such county probation officer shall have reached the age of sixty years or not, shall receive a pension, so long as she shall remain unmarried, equal to one-half the amount of the annual salary of such county probation officer at the time of his death; and upon the death of such widow, or in the event there be no widow, the child or children of such probation officer, under the age of sixteen years shall, until each reaches the age of sixteen years, receive the proportionate amount of such pension.