This arm will complete treatment as usual during the 4 months of the study. Specifically, if the family is receiving any intervention, they will continue to receive it. Once the post-treatment study visit is completed, they will be granted access to the intervention being studied (OPT-In-Early)

The intervention group will receive access to OPT-In-Early. OPT-In-Early is an online 14-module self-directed parent-training program that uses simple text, narration, and interspersed videos to teach parents how to increase their children's social engagement, communication, adaptive behaviors, and reduce challenging behaviors.

OPT-In-Early is an online 14-module self-directed naturalistic developmental behavioral intervention (NDBI) that uses simple text, narration, and interspersed videos to teach parents how to increase their children's social engagement, communication, adaptive behaviors, and reduce challenging behaviors.

We will administer a revised Motor Imitation Scale (MIS), a standardized, structured observational measure that assesses a child's ability to imitate familiar and novel motor actions. Children will see 5 actions modeled and then will be prompted to imitate the action using a matching toy. Children are given up to three opportunities to imitate each action. MIS scores range from 0 to 10, with higher scores indicating greater imitation.

The Vineland Scales of Adaptive Behavior-3 (Vineland-3) is a standardized parent interview measuring adaptive functioning. It will be administered to all participants at pre- and post-treatment to evaluate change occurring in adaptive behavior across groups. Previous research has documented that this measure has robust psychometric properties, is sensitive to change in response to early intervention, and captures dimensions that are highly valued by stakeholders. Higher scores in the Vineland indicate more advanced adaptive skills.

The MacArthur Bates Communication Development Inventory (MCDI) is a parent-report measure that assesses nonverbal communication (gestures) and verbal communication (words). The Words and Gestures form will be used. The MCDI is widely used, standardized, and validated. It is particularly well-suited for large-scale research due to ease of administration, strong psychometric properties, and sensitivity to individual differences in early language development. Higher scores indicate greater communication.

The Goal Attainment Scaling (GAS) is used to evaluate a participant's progress toward a specific, individualized goal. It follows standardized procedures that allow outcomes to be measured on a common metric, making it possible to compare intervention-related change across participants with different goals. Scores ranger from -2 to +2, with higher scores indicating better functioning.

Parents randomized to the intervention group will complete time-based ecological momentary assessment (EMA). EMA will be used to obtain parent report about whether they (a) reviewed a module (yes/no); (b) practiced learned skill with their child (yes/no); and (c) the duration spent practicing skills with their child (minutes)