Avoidant Restrictive Food Intake Disorder (ARFID) is a newly articulated eating disorder in the DSM-5 in which individuals are not able to consume an adequate quantity or variety of food to sustain healthy growth and de- velopment. ARFID typically onsets in early childhood, yet identification of the disorder is poor. The end result is that children often have sustained inadequate nutrition with resulting severe physical consequences and threats to optimal social and emotional development. Early intervention is essential. However, there are no em- pirically validated treatments for young children with ARFID. Children with ARFID are known to be sensitive individuals: with a low threshold for noticing internal body sensations (e.g., gastrointestinal distress) and exter- nal sensory sensations (e.g., smells) and experiencing these sensations as uncomfortable/aversive. This sen- sitivity, and the associated negative emotional reactions (e.g., of disgust, fear, sadness), may encourage avoidance of activities that cause these sensory experiences, such as eating. An intervention that could change reactions to sensory and somatic sensations to one of playful curiosity may increase approach behav- ior and food consumption. We designed an acceptance-based interoceptive exposure treatment for children to achieve this goal. We teach children and caregivers to be “FBI Agents,” individuals who view somatic and sen- sory sensations as clues to a mystery via the use of engaging illustrative cartoon characters (e.g., Gassy Gus), body investigations that provoke intense sensations and worksheets that map sensations to meanings and ac- tions. The goal is to make somatic and sensory experiences playful – and to promote adaptive self-awareness and food approach. The overall objective of this study is to determine whether treatment results in reduced negative emotions to somatic and sensory sensations, including those associated with food and eating, and whether this, in turn, increases food approach. This will be accomplished by a randomized controlled trial (N = 140, 70 per cell) comparing The Feeling and Body Investigators (FBI) - ARFID Division treatment, a 20-session outpatient treatment, to a control group in children (5 to 9 years of age) with ARFID. The control treatment (FAD: Family-Assisted Diet) will provide family-supported exposure. Our proposed mediator of treatment re- sponse is negative affect: a child’s facial affect in response to food presentation as measured via smartphone videos. Outcomes include changes in anthropometric measurements, nutrition variety and adequacy, and psy- chosocial functioning. Medical and psychological measurements will be assessed pre- and post-treatment, at every session, and 3-month follow-up. Deliverables include an empirically validated treatment(s); medical guidelines for the early detection of insufficient nutrition; practical tools for assessing food acceptance in the home via smartphones; and guidance about the number...