Loop in a page from a category and relative child (with a counter)

How can i get a loop inside a page with the posts from a specific catagory and all his relative child?

I also need a “counter” because i want the last 4 posts. Then i place a div with a adv banner. After that i want to restar showing the next 4 posts.

I’ve tried that but it seems not working, https://pastebin.com/jc4SQHkc

Anyone can help me out?

Thanks