Purpose <p>In Aotearoa New Zealand (NZ), families face persistent barriers to accessing evidence-based early support for Autistic children. This randomized controlled trial (RCT) evaluated the effectiveness of Let’s Play; a bespoke, caregiver-mediated early support program for Autistic children and their caregivers.</p> Methods <p>This single-blind (rater) RCT included 91 parent-child dyads, randomly assigned to the Let’s Play program (active support; AS [<i>n</i> = 45]) or a waitlist control (WLC; <i>n</i> = 46). Participants were caregivers of children aged 0 to 5 years with a formal diagnosis or characteristics of autism. Let’s Play was delivered over 9 weeks via group workshops and in-home coaching. Primary child and caregiver outcomes, assessed at baseline, post-support, and 6-month follow-up, included parent-child engagement and parental stress, respectively.</p> Results <p>Children showed descriptive evidence of improvement in caregiver-child engagement, health-related quality of life and behaviour from baseline to post-support. Improvement in parental stress, depression and anxiety symptoms, and self-perceived parenting competence were also evident, across timepoints. However, there were no significant Group x Ttime effects for caregiver-child engagement, number of utterances or number of different words. A Group x Time effect was evident for all other child and caregiver outcome variables, underscoring the benefits of Let’s Play.</p> Conclusions <p>This research provides preliminary evidence of the effectiveness of a low-intensity, community-based, caregiver-mediated early support program for Autistic children’s health-related quality of life and behavior and caregiver well-being. However, more targeted or sustained approaches to supporting caregiver-child engagement and vocal communication may be needed for improvement to be observed.</p> Clinical Trial Registration <p>The research protocol was prospectively registered on the Australian New Zealand Clinical Trials Registry (ACTRN12622001139763).</p>