Most U.S. children grow up with siblings. Theory and prior work suggest that older siblings are important sources of gender-related information and socialization. However, few studies have investigated the patterns of these associations longitudinally across early childhood. The present study examines the influence of sibling presence and gender composition on the trajectory of early gender-typed behavior and appearance in children from age 2 through 6 in a diverse sample of Dominican American (36%), African American (33%), and Mexican American (31%) mother-child dyads (N = 232; 112 girls, 120 boys) from low-income households in New York City (M = $20,459, SD = 14,632). Results found that children without older siblings spent more time playing with counterstereotypical toys and their mothers' reports indicated similar behavior over the past month (e.g., a girl playing with toy vehicles and balls; a boy playing with toy kitchen sets and dolls) than children with older siblings. Further, children with at least one other-gender sibling (e.g., a girl with an older brother) played more frequently with counterstereotypical toys compared with children with only same-gender siblings (e.g., a girl with only older sisters). Results on the relation between siblings and gender appearance were mixed. Older siblings may thus influence early trajectories of important gender domains (e.g., toy play), which can have various long-term implications for developing skills and interests. (PsycInfo Database Record (c) 2021 APA, all rights reserved).