A benefit shall be granted to any child of the employee under 18 years of age or any child under such age legally adopted by the employee whose death occurred under the following conditions:
In the case of an employee whose death occurs after withdrawal subsequent to age 55, if eligible for an annuity, birth of a child must have occurred before the date of the employee's latest withdrawal.
No annuity shall be payable to any child after such child's marriage. The termination date of any child's annuity due to the attainment of age 18 or marriage shall be the due date of the last annuity payment for the child, next preceding such due date with no proration for any period which is less than a full month.
A posthumous child shall be regarded as a child of the employee entitled to an annuity.
40 ILCS 5/12-137