wmig

This simple plugin will hide posts from children categories.
It just override include_children property for hierarchical taxonomies.

Exclude Children

This simple plugin will hide posts from children categories

ymonica32

This plugin allows you to display checked categories in hierarchical order. Selected categories will remain in their defined order rather than moving to the top of the list. 
It helps maintain the structure of parent and child categories in the post editor, making it easier for users to follow the taxonomy hierarchy when assigning categories.

WP Category Order

Display WordPress post categories in parent–child hierarchy while editing posts in the admin panel

Exclude Children vs WP Category Order