customize child record on master table edit page

Here is my situation: I have a master table and a child record. My setting is display child records on master table edit page. It is just exactly what I needed.
And here comes the problem:

My child record has 7 fields in which 5 fields are in text format. My problem is I can't put each field in a separate line like the master table. Instead, each records (with 7 fields) shows in one row which make the whole page stretch horizontally all the way to the right.
So, what I want is to separate each field by line so it won't affect the width that I set for the form.
Please help if you have any idea to solve this problem.
Thank You.

LH