Dependent benefits shall be paid to each natural child of a deceased firefighter, and to each child legally adopted, until the child’s attainment of age 18 or marriage, whichever occurs first, whether or not the death of the firefighter occurred prior to November 21, 1975.
     Benefits payable to or on account of a child under this Article shall not be reduced or terminated by reason of the child’s adoption by a third party after the firefighter’s death.
     Benefits payable to or on account of a child under this Article shall not be reduced or terminated by reason of the child’s attainment of age 18 if he or she is then dependent by reason of a physical or mental disability but shall continue to be paid as long as such dependency continues. Individuals over the age of 18 and adjudged as a disabled person pursuant to Article XIa of the Probate Act of 1975, except for persons receiving benefits under Article III of the Illinois Public Aid Code, shall be eligible to receive benefits under this Act.