Follow this link to see how to add a guardian to your primary account.
https://help.sportsengine.com/en/articles/6304039-how-to-add-guardians
If you are a head coach or team manager you can also add guardians follow this link to see how.
https://help.sportsengine.com/en/articles/6417497-how-to-add-a-guardian-to-a-player-s-profile-using-the-mobile-app