Your 'Elf Passcode' is a 4 digit code that you create when you set up the Call app for the first time. It ensures that your children cannot view any scheduling information and preserves the "mystery" just in case they open our Santa app. However, kids will still be able to listen to their past messages and share with family and friends without the passcode.
You will be prompted to create your own passcode. Please check the email address you entered. It's possible that you may have used a different email address when installing the APP.