Numerous states require parental notification, consent, or involvement in police interrogations of juvenile suspects, presumably to advocate for youths' rights and protect against police coercion. Such laws presuppose that parents possess the knowledge, capacity, and inclination to serve this protective function, yet little is known about parents' understanding of interrogation rights and procedures or their decision making in juvenile interrogations. This study tested a geographically diverse sample of parents' (N = 515) knowledge about youths' interrogation rights, their awareness of police interrogation practices, and their advisements to youth regarding Miranda waiver across three different custodial contexts using vignettes about custodial questioning of a presumably guilty adolescent. The study experimentally manipulated the nature of the police encounter (i.e., police contact originating as a street stop, with parents facilitating interrogation, or with arrest) as well as the target youth's age (13, 15, or 17 years). Parent interrogation knowledge differed by custodial context, with parents least accurate in parent-specific vignette situations and on knowledge items specifically related to parent involvement. Almost all parents expressed a desire to participate in the Miranda waiver decision, with about 65% encouraging youth to remain silent and 30% encouraging youth to talk to police. Overall, findings provide evidence that parents are poorly situated to play a protective role in juvenile interrogations.