Upon the death of a member prior to retirement who was a member continuously for not less than 18 months immediately prior to his death and who is survived by one or more children, during such time as no eligible spouse is entitled to a survivor’s allowance pursuant to this article, if the father or mother having custody or guardian of such child or children waives the amount, if any, payable as a death benefit pursuant to Section 31781, such child or children shall be entitled to a monthly survivor’s allowance equal to the sum, based upon the member’s compensation at the time of his death and the number of children, specified in Section 31849 minus the amount to which such

children are entitled pursuant to Section 31765, 31765.1, 31781.1, 31781.2, or 31787.