20 CFR 222.31: Relationship as child for annuity and lump-sum payment purposes.

(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) The natural or legally adopted child of the employee (see § 222.33); or

(2) The stepchild of the employee; or

(3) The grandchild or step-grandchild of the employee or spouse; or

(4) The equitably adopted child of the employee.

(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) The natural child of the employee;

(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) 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.