This rigorous randomized controlled trial will evaluate the efficacy and acceptability of a preemptive, telehealth intervention (tele-ImPACT) in a large, representative sample of infant siblings of autistic children, who are known to be at high likelihood of receiving a future diagnosis of autism and/or developmental language disorder (HL-Sibs). If our hypotheses are supported, this innovative and interdisciplinary study will provide empirical support for a novel approach to treatment that is theoretically motivated and developmentally informed, as well as accessible for and acceptable to families, and will lend new insights into the developmental windows in which, mechanisms by which, and subgroups for which the treatment works. Such findings would have strong implications for research, policy, theory, and practice in young children at risk for autism and/or language disorder.