To obtain legal guardianship over an adult child with disabilities, a parent must file a petition in the local court. This process typically involves gathering necessary documents, including a Letter of Legal Guardianship with Adults with Disabilities, which outlines the need for guardianship. After submitting the petition, a hearing will be scheduled where the court evaluates the case. If the court approves the petition, it will grant legal guardianship, allowing the parent to make decisions on behalf of their adult disabled child.