To explore the ways in which Latinx older siblings support younger siblings during shared reading, researchers investigated the following question with three Latinx families in the U.S.: "How are older siblings modeling and intentionally supporting focal children's cognitive self-regulation in the context of shared reading?" Analyses of video recorded interactions across six visits revealed that older siblings intentionally supported focal children's cognitive self-regulation by fostering autonomy and choice through the use of verbal and nonverbal cues to guide attention, using prosody to engage their sibling, and to initiate reading beyond resistance, and vicarious modeling of metacognitive processes by engaging in self-corrections and demonstrating positive affect during shared reading interactions. Findings highlight the importance of older siblings, particularly sisters, as key figures in the sociocultural context of development for Latinx younger siblings in the U.S.