20 CFR §222.31

1. (a)Annuity claimant. When there are claimants under paragraph (a)(1), (a)(2), or (a)(3) of § 222.30, a person will be considered the child of the employee when that person is—
   1. (1)The natural or legally adopted child of the employee (see § 222.33); or
   2. (2)The stepchild of the employee; or
   3. (3)The grandchild or step-grandchild of the employee or spouse; or
   4. (4)The equitably adopted child of the employee.
2. (b)Lump-sum payment claimant. A claimant for a lump-sum payment must be one of the following in order to be considered the child of the employee:
   1. (1)The natural child of the employee;
   2. (2)A child legally adopted by the employee (this does not include any child adopted by the employee's widow or widower after the employee's death); or
   3. (3)The equitably adopted child of the employee. For procedures on how a determination of the person's relationship to the employee is made, see §§ 222.32-222.33.