To view child records in the web app you can use the app selector at the top of the web app's record editor to select the repeatable section you would like to view the child records for.
Note: It doesn't really matter which app you use to get to the record editor, since you will be changing the view to a repeatable section once you are on the record editor.
To view the child records, start on the homepage then:
Click the records icon to go to the record editor to view the data collected.
On the record editor, click on the name of the app that you are viewing.
Locate and select the repeatable section you would like to view the child records for.