lived, shall be paid to the deceased retired member’s child or children under the age of 18 years. If the survivor allowance is to be paid to surviving children, the allowance shall be divided among the children in equal amounts. However, the right of any child to share in the allowance shall cease upon his or her death, marriage, or upon attaining the age of 18 years.

Notwithstanding any other provisions of this subdivision, the allowance otherwise payable to the children of the retired member shall be paid to the children through the age of 21, if the children remain unmarried and are regularly enrolled as full-time students in any accredited school as determined by the board.

retirement applied to a lesser amount payable throughout the retired member’s life, and thereafter to have a survivor allowance as approved by the board, upon the advice of the actuary, continued throughout the life of and paid to the person or persons having an insurable interest in the life of the retired member, as the member or former member nominates by written designation duly executed and filed with the board at the time of retirement.