Hi Melonie

Totara does expect unique usernames - you can make up an email address as  the username is not used for sending any emails - it is the users email field that is used for this. 

Using the upload users feature to create users you can set the allow duplicate emails setting so the parent gets any e,mails related to their children.

For progress to be stored against each child each child needs a unique username.

Assigning the parent as the manager of their children allows the parent to login and see the progress of each of the children they manage through the Team menu.

Regards