20 CFR § 404.363
When is a stepchild dependent?
February 18, 2021
If you are the insured's stepchild, as defined in §404.357, we consider you dependent on him or her if you were receiving at least one-half of your support from him or her at one of these times—
(a) When you applied;
(b) When the insured died; or
(c) If the insured had a period of disability that lasted until his or her death or entitlement to disability or old-age benefits, at the beginning of the period of disability or at the time the insured became entitled to benefits.
[44 FR 34481, June 15, 1979, as amended at 75 FR 52621, Aug. 27, 2010]