Improving social communication outcomes for toddler siblings of children with autism, who are at high risk for multiple language and communication deficits beyond autism, has important public health implications. The proposed study is a pilot sequential multiple random assignment trial of 44 high-risk siblings that examines the feasibility, acceptability, and preliminary effects of an adaptive intervention for social communication. Evaluating effective parent-mediated communication support strategies for toddlers at high-risk supports NIDCD's mission of behavioral research focused on disordered language development and the prevention of health impairments such as communication disorders.