20 CFR § 404.330 - Who is entitled to wife's or husband's benefits.
(1) Your relationship to the insured as a wife or husband has lasted at least 1 year. (You will be considered to meet the 1-year duration requirement throughout the month in which the first anniversary of the marriage occurs.)
(2) You and the insured are the natural parents of a child; or
(3) In the month before you married the insured you were entitled to, or if you had applied and been old enough you could have been entitled to, any of these benefits or payments: Wife's, husband's, widow's, widower's, or parent's benefits; disabled child's benefits; or annuity payments under the Railroad Retirement Act for widows, widowers, parents, or children 18 years old or older;
(c) You are age 62 or older throughout a month and you meet all other conditions of entitlement, or you are the insured's wife or husband and have in your care (as defined in §§ 404.348 through 404.349), throughout a month in which all other conditions of entitlement are met, a child who is entitled to child's benefits on the insured's earnings record and the child is either under age 16 or disabled; and