If you can't login, check that your child's phone is linked to your email. This can be checked on the phone by going to settings > SafetyMode settings > settings and checking your email appears in the "Parent Account" section.
If you need to update this email, tap "Connect Email Account". If you don't see that option tap "Disconnect" to remove the current email.
Once connected, try logging in again using your parent email.
Still having issues? Contact [email protected].