Displaying only specific categories in today's active threads/view new posts

[TJF]

I'm using 3.8.11. I've searched for an answer, but I haven't found on how to what I want. A few people have asked similar questions in the past.

My forums structure is categories with many sub-forums.

Forum 1
--- Forum 2
--- Forum 3
--- Forum 3
--- Forum 4

I know you can include or exclude specific forums by adding &include=1,2,3,4 or &exclude=1,2,3,4. Is there a limit on how many forums you can include/exclude?

I read in a post on here that you can add &child=1 and it would display only the child forums, but it doesn't seem to work.

I want to make custom searches that will display all the new posts from the sub-forums of Forum 1. Is it also possible to set up a category and display all the sub-forums posts under one category?

I have it set up this way:

Depth of Forums - Forum Home - 1
Depth of Forums - Forum Display - 1
Depth of Sub-Forums - 1

I want to display all posts under one category, but keep the individual forums structure.