Yahoo! has ceased the creation of new Yahoo! Family Accounts, which were previously used to create email accounts for kids younger than 13. Because of this, Bark does not recommend using Yahoo! email with younger kids.
If you would like to monitor your 13+ child’s Yahoo! email account, another option would be to know the password to it and log in frequently to check what your child has been sending/receiving. This method, however, can be bypassed if your child deletes messages.