20 C.F.R. § 404.731
If you are the natural parent of the insured person, we will ask for a copy of his or her public or religious birth record made before age 5. If you are the natural child of the insured person, we will ask for a copy of your public or religious birth record made before age 5. In either case, if this record shows the same last name for the insured and the parent or child, we will accept it as convincing evidence of the relationship. However, if other evidence raises some doubt about this record or if the record cannot be gotten, we will ask for other evidence of the relationship. We may also ask for evidence of marriage of the insured person or of his or her parent if this is needed to remove any reasonable doubt about the relationship. To show you are the child of the insured person, you may be asked for evidence you would be able to inherit his or her personal property under State law where he or she had a permanent home (see § 404.770 ). In addition, we may ask for the insured persons signed statement that you are his or her natural child, or for a copy of any court order showing the insured has been declared to be your natural parent or any court order requiring the insured to contribute to you support because you are his or her son or daughter.
20 C.F.R. §404.731