Delete your Wunderkind account
In the app
Sign in as the grown-up, tap "Delete account" at the bottom of the screen and confirm. It takes effect straight away and removes the parent email address, every kid profile and all watch history.
Without the app
Email maros.pristas@gmail.com from the email address of the account, with the subject "Delete my Wunderkind account". It is done within 7 days.
What is kept
Nothing is kept afterwards except server backups, which roll off within 30 days.