20 C.F.R. § 404.355
Who is the insured's natural child?
(a) Eligibility as a natural child. You may be eligible for benefits as the insured's natural child if any of the following conditions is met:
(1) You could inherit the insured's personal property as his or her natural child under State inheritance laws, as described in paragraph (b) of this section.
(2) You are the insured's natural child and the insured and your mother or father went through a ceremony which would have resulted in a valid marriage between them except for a “legal impediment” as described in § 404.346(a).
(3) You are the insured's natural child and your mother or father has not married the insured, but the insured has either acknowledged in writing that you are his or her child, been decreed by a court to be your father or mother, or been ordered by a court to contribute to your support because you are his or her child. If the insured is deceased, the acknowledgment, court decree, or court order must have been made or issued before his or her death. To determine whether the conditions of entitlement are met throughout the first month as stated in § 404.352(a), the written acknowledgment, court decree, or court order will be considered to have occurred on the first day of the month in which it actually occurred.
(4) Your mother or father has not married the insured but you have evidence other than the evidence described in paragraph (a)(3) of this section to show that the insured is your natural father or mother. Additionally, you must have evidence to show that the insured was either living with you or contributing to your support at the time you applied for benefits. If the insured is not alive at the time of your application, you must have evidence to show that the insured was either living with you or contributing to your support when he or she died. See § 404.366 for an explanation of the terms “living with” and “contributions for support.”
(b) Use of State Laws—(1) General. To decide whether you have inheritance rights as the natural child of the insured, we use the law on inheritance rights that the State courts would use to decide whether you could inherit a child's share of the insured's personal property if the insured were to die without leaving a will. If the insured is living, we look to the laws of the State where the insured has his or her permanent home when you apply for benefits. If the insured is deceased, we look to the laws of the State where the insured had his or her permanent home when he or she died. If the insured's permanent home is not or was not in one of the 50 States, the Commonwealth of Puerto Rico, the Virgin Islands, Guam, American Samoa, or the Northern Mariana Islands, we will look to the laws of the District of Columbia. For a definition of permanent home, see § 404.303. For a further discussion of the State laws we use to determine whether you qualify as the insured's natural child, see paragraphs (b)(3) and (b)(4) of this section. If these laws would permit you to inherit the insured's personal property as his or her child, we will consider you the child of the insured.
(2) Standards. We will not apply any State inheritance law requirement that an action to establish paternity must be taken within a specified period of time measured from the worker's death or the child's birth, or that an action to establish paternity must have been started or completed before the worker's death. If applicable State inheritance law requires a court determination of paternity, we will not require that you obtain such a determination but will decide your paternity by using the standard of proof that the State court would use as the basis for a determination of paternity.
(3) Insured is living. If the insured is living, we apply the law of the State where the insured has his or her permanent home when you file your application for benefits. We apply the version of State law in effect when we make our final decision on your application for benefits. If you do not qualify as a child of the insured under that version of State law, we look at all versions of State law that were in effect from the first month for which you could be entitled to benefits up until the time of our final decision and apply the version of State law that is most beneficial to you.
(4) Insured is deceased. If the insured is deceased, we apply the law of the State where the insured had his or her permanent home when he or she died. We apply the version of State law in effect when we make our final decision on your application for benefits. If you do not qualify as a child of the insured under that version of State law, we will apply the version of State law that was in effect at the time the insured died, or any version of State law in effect from the first month for which you could be entitled to benefits up until our final decision on your application. We will apply whichever version is most beneficial to you. We use the following rules to determine the law in effect as of the date of death:
(i) If a State inheritance law enacted after the insured's death indicates that the law would be retroactive to the time of death, we will apply that law; or
(ii) If the inheritance law in effect at the time of the insured's death was later declared unconstitutional, we will apply the State law which superseded the unconstitutional law.