After consent, participants will complete an in-person lab-based sensory responsivity protocol which measures the child's responsivity to standardized sensory stimuli. Questionnaires and training on the home-based data collection protocol will also be completed. A short interview or survey regarding the lab-based protocol will be completed. After the lab visit, the child and caregiver will wear an actigraphy watch and complete daily diaries about sleep and emotion for two weeks. Upon the completion of these two weeks, the participants will return to the lab to be trained in the Power Down Protocol. Then the child and caregiver will engage in a 2-week intervention trial. Upon completion, participants will complete exit questionnaires and interviews.

After consent, participants will complete an in-person lab-based sensory responsivity protocol which measures the child's responsivity to standardized sensory stimuli. Questionnaires and training on the home-based data collection protocol will also be completed. A short interview or survey regarding the lab-based protocol will be completed.

After the lab visit, the child and caregiver will wear an actigraphy watch and complete daily diaries about sleep and emotion for two weeks. Upon the completion of these two weeks, the actigraphy watches are returned and final questionnaires are completed.

The Power Down is a bedtime manipulation protocol targeting elevated arousal level at bedtime due to a hypothesized effect of sensory over-responsivity (a common experience for autistic children). The Power Down incorporates sensory-based input (caregiver massage) to support nervous system regulation prior to attempting sleep onset. Participants (caregivers and their child) will be educated in the Power Down protocol and data collection methods for the 2 week intervention trial. Caregivers will lead a nightly gentle massage with guided relaxation script just prior to the child trying to fall asleep. The child will also wear a watch-like activity monitor for the 2 week period throughout the day and night to measure changes in sleep and activity patterns. Caregivers will complete daily diary questions in the morning and evening reporting their child's emotions and sleep timing.

Average of nightly questions related to bedtime emotion dysregulation, based on Emotion Dysregulation Inventory short form, presented through the nightly sleep diary. The Emotion Dysregulation Inventory short form is 13 questions and scaled using a 5-point scale of "very severe" to "not at all" with higher scores indicating higher endorsement of each item. Average nightly scores range from 1-5. Measured across baseline (2 weeks) and intervention period (2 weeks).

Average of nightly question within the sleep diary related to child's sensory over-responsivity behaviors during bedtime on a scale of 0-100 where larger number indicates more evidence of sensory over-responsivity, 50 indicates typical response, and lower numbers indicate less evidence of sensory over-responsivity. Averages will be collected nightly across baseline (2 weeks) and during the intervention period (2 weeks).

Using reported "start of settling down" from daily sleep diaries and data from the actigraphy watch, sleep onset latency will be calculated and assessed for the child across the 2 week baseline and 2 week intervention period.

Change in sleep efficiency (calculated as a ratio of total sleep time to duration of sleep episode) between baseline and during intervention period