Scroll to the bottom of the page and log into the Parental Controls.
Next, under the Summary section press the "Add Accounts" button.
To add a completely new account, select "Make New Account" and make a username and password. Don't forget to press "Add Account". Once a sub account is added it can not be unlinked from the family account.
Another option you have is to add an Existing Account as a sub account. To do this select this option and then put in the username and password of the account you would like to add. Press "Add Account".
Once you have all the accounts added to your Family of Accounts, you should see an updated "My Accounts" screen, showing the new sub-account(s).
*IMPORTANT NOTE* When you create a Family of Accounts, each account is still considered an individual account for billing and account settings purposes. For Instance, if the Family Master is subscribed the subscription does not apply to the Sub accounts. Each of those accounts must subscribe individually to have advanced access. Also, once a family account is created and accounts are added to them we are unable to unlink the sub accounts or switch which account is the family master.