Is there a way to change the child generated by WordPress itself to a custom class name?
I know the parent
To change the default "sub-menu" class name, there is simple way. You can just change it in wordpress file.
location : www/project_name/wp-includes/nav-menu-template.php.
open this file and at line number 49, change the name of sub-menu class with your custom class.
Or you can also add your custom class next to sub-menu.
Done.
It worked for me.I used wordpress-4.4.1.