How the get all the child menu's Node IDs?
I think you're approach is just from the wrong end, the menu is just a list of links and not meant to control content.
What you want to do is:


Make "Company" as a views > page or a views blocks within etc.
Make a taxonomy reference for the sub pages or make them separate entity or content type,  in order to specify your sub pages in views.
Create view_mode like teaser to format their subpage display.