You can create a profile from the Profiles tab within the Parents section of the app or use the SIGN IN tab on the home page. You'll need an email address and a password to create an Profiles. Keep an eye out for an email with your verification code to complete your Profiles setup.
In order to share your subscription across multiple devices, you will need to create a Scribble Scrubbie Pets Profile and then login to that Profile using your login credentials. Your subscription access is tied to the app store account that purchased the subscription, so ensure you are logged into your profile with that device/app store account.