If you know the category… just use PARENT in the query- e.g. PARENT = Cars
You can select the term from a menu.
If you want all children of the current category (e.g. you’re on an archive page and want to show parent cats of the current cat). Then put {term_id} in the PARENT field in your query.
Okay, so I now see what @digismith was trying to say. but 0 only returns the parent, in the example above what @dushyanth wanted was to get the “first level sub”. For this to work you have to know the ID of the parent category, in this case, cars and put it in the parent field in the query builder loop e.g. let’s say the cars category ID is 32 then when you put it in the parent field you’ll get Hatchback, Sport, Commute, Tuned … I found the answer here:
tern query section