A computer-implemented method for enforcing access-control policies may include (i) identifying streaming content that is being transmitted from a media server to a media playback system, (ii) determining that a supervised user is within exposure range of the media playback system and could be exposed to the streaming content, (iii) receiving a sample of the content from a sampling system that is remote from the media playback system, (iv) identifying an access-control policy that defines a content-access restriction for the supervised user, (v) determining, based on an analysis of the sample of the content, that the access-control policy applies to the content, and (vi) in response to determining that the access-control policy applies to the content, enforcing the access-control policy by applying the content-access restriction to the streaming content. Various other methods, systems, and computer-readable media are also disclosed.