How to upload element data with sub-elements in sharepoint?

Question

SharePoint

Hello.
I have sharepoint 2013 foundation.
Suppose there is a list "Order" and a subordinate list "OrderString".
When entering an order, I see the lines of this order and, with the help of a special link and minor editing of the new page, I can create a new line that immediately belongs to this order.
How to export this order to a file? As far as I was able to do, I can only export the order itself, not its lines.
You can, of course, write a program in c # that will connect to the server, select an order and all its children, and generate the xml for the merge itself, but in my opinion, this is somehow far-fetched.