b. No Surviving Spouse and Surviving Children. Subject to paragraph c., if a participant dies as a result of injuries received in the line of duty and leaves no surviving spouse or the surviving spouse should die, and if the participant leaves a surviving child or children under the age of 18 years at the time of the participant's death, the retirement board shall direct the payment to the legal guardian of such child or children, for the use and benefit of the child or children, until the youngest child reaches the age 18 years, a monthly death benefit equal to 62 1/2 percent of the participant's monthly benefit calculated in accordance with Section 45-8A-22.113 using a period of 25 years of continuous service regardless of the participant's actual number of years of continuous service. As each child attains, or in the event the child dies before attaining, the age of 18 years, the child shall cease to participate in the monthly death benefits, thereby increasing the share or shares of the other child or children under the age of 18 years.