The concept is, portal can show records from only one table.
You need creating all parent and child records in a table.
To expand on what you are being told in every forum where you have posted this request: this information belongs in one table.
If you look at literal human parent child relationships, then (again) there is ONE table.
Every record has a unique ID. In addition, foreign keys fk_Mom and fk_Dad.
It is a "People" table. There is no "Parents" table.
Or you use two portals, one to list the parents and one to list the child records of a selected parent where you click the parent row and a script updates a field such that only the child records for the selected parent appear in the second portal.
A list view layout based on parent can include a portal to Child. this will look much like what you describe here.
A list view layout based on Child can include fields from Parent in a sub summary layout part and if you then sort by parent, you get the layout that you describe.
A portal to Child can include both Parent and Child fields if the relationship is set up correctly. A Hide Object When condition can hide data from Parent except for the first Child record for that Parent--but this can be a bit tricky to do.