This randomized controlled trial (NCT03889821) examined Mindfulness Based Stress Reduction (MBSR) in conjunction with the Parent-implemented Early Start Denver Model (P-ESDM). A previous report described improved metrics of parental distress (Weitlauf et al. in Pediatrics 145(Supplement 1):S81–S92, 2020). This manuscript examines child outcomes. 63 children with ASD (< 36 months) and their parents received 12 P-ESDM sessions. Half of parents also received MBSR. Longitudinal examination of whole sample means revealed modest improvements in autism severity, cognitive, and adaptive skills. There was not a significant time × group interaction for children whose parents received MBSR. Future work should examine more proximal markers of child or dyadic change to enhance understanding of the impact of providing direct treatment for parents as part of early intervention initiatives.