Button to Add Child Record, Save it, Display it, Reload, then Edit mode
I have a button that adds an Estimate to an Opportunity. The button Adds the child record, Saves it, and Displays it. An automation runs in the background that adds child records to the Estimate. Idea...
Another technique is to put the child table report link in a tab. By the time the user clicks the tab, the automation will have run and the children will be there.