20 C.F.R. § 219.36 – When evidence of a parent or child relationship is required.

(a) When parent or child applies. A person who applies for a parent's or child's annuity or for Medicare coverage is required to submit evidence of his or her relationship to the deceased employee.
(b) When individual with child in care applies. An individual who applies for an annuity because he or she has a child of the employee in care is required to submit evidence of the child's relationship to the employee.
(c) Evidence required depends on relationship. The evidence the Board will require depends on whether the person is the employee's natural child, adopted child, stepchild, grandchild, or stepgrandchild; or whether the person is the employee's natural parent or adopting parent.