If you as a parent want to change your login details, go to "Settings" β "About me". There you can change your name, your e-mail and your telephone number.
If you are a parent and want to change the child's login details, go to "Settings" β "My children" β (The child you want to change) β "General settings"
If you are logged in to a child account, press the wrench in the top right corner of the main menu. Then tap on "About Me".