If they are not in the database, read this article on how to add new members:
Login to your Club Control Panel.
Click the Membership tab.
Click Membership Database in the left side menu.
Find the Parent in the database using the search and filter tools.
Click on the parents name to bring up the members details.
Click the Roles tab.
Tick the box next to Parent and type the name of the child into the search box.
Click on the child's name from the list and click Save.