20 C.F.R. § 222.57
An employee's equitably adopted child, as defined in § 222.34 , is considered dependent upon the employee if the employee was either living with or contributing to the support of the child at the time of his or her death. If the equitable adoption is found to have occurred after the employee could have become entitled to an old age or disability benefit under the Social Security Act (treating his or her railroad compensation as wages under that Act), the child is not considered dependent on the employee during the employee's lifetime. If the equitable adoption took place before such time, the child is dependent on the employee if the employee was living with or contributing to the support of the child at one of the times shown in § 222.51 .
20 C.F.R. §222.57