20 C.F.R. § 404.350
Who is entitled to child's benefits?
(a) General. You are entitled to child's benefits on the earnings record of an insured person who is entitled to old-age or disability benefits or who has died if—
(1) You are the insured person's child, based upon a relationship described in §§ 404.355 through 404.359;
(2) You are dependent on the insured, as defined in §§ 404.360 through 404.365;
(3) You apply;
(4) You are unmarried; and
(5) You are under age 18; you are 18 years old or older and have a disability that began before you became 22 years old; or you are 18 years or older and qualify for benefits as a full-time student as described in § 404.367.
(b) [Reserved]