get_stylesheet_directory() in child theme breaks parent scripts

The problem your facing here can be solved by changing the function being used:

• get_stylesheet_directory will give you the directory of the current active theme, aka the location of the active style.css
• get_template_directory will give you the directory of the active theme, aka the parent theme

For most themes the two give the same result, but:

• Always use get_stylesheet_directory when referring to things in a child theme
• Always use get_template_directory when in a parent theme
• Always use get_template_part to load a template, never use the previous 2 function
• Use include and require to load a file that doesn’t contain a template such as a class or PHP include. If you need to override these, use hooks and actions to do this via remove_action etc
• Minimise any cross talk between child themes and parent themes. A child theme shouldn’t be attempting to include files in a parent theme etc other than through get_template_part