The purpose of this study is to understand how cognitive function changes over time in children with hyperinsulinism (HI) compared to children who are healthy volunteers. Participants will be asked to complete cognitive function tasks and questionnaires three times over the course of two years: at the start of the study, one year later, and one year after that. Each visit is approximately 2 hours. If you like, you can receive a summary of the results from the tasks. Compensation is provided for your time and effort.