Adults cannot be friends with kids unless they are a Guardian or ChessKid staff. Check out this article to learn how to become your Kid's guardian: How To Connect To My Kid Through Guardianship
ChessKid uses a blind friend request system, which means your child will not receive notifications for friend requests. A friend will only be added if your child also sends a request to that user, ensuring they know each other in real life and preventing careless additions.
In addition, Parent and Coach accounts can Impersonate their kids to keep track of all correspondences, friends, and other behavior.
How to impersonate my kid
From your parent account click Manage on the menu at the top and select Kids:
Click on the icon next to the Kid account you'd like to see and select Impersonate:
Once logged into their account, click on Connect in the menu on the left side and select Friends to view and manage your kid's friends. You can also cancel any sent friend requests that haven't yet been accepted: