The Parent of Alumni role is only given to parents when the Parental Access flag is enabled on their Parent/Child relationship

If a Parent of Alumni does not have the Parent of Alumni Role, follow these steps to add it:
  1. Navigate to Core > People Finder > Search for and select the Parent
  2. Go to the Contact Card tab
  3. Under relationships, click Manage
  4. Next to their child, mark the Parental Access box
  5. Click save