To drill down from Parent to Child:
1. Group on Parent.
2. Create another group on Child.
3. Place your fields and summaries as you want them to appear on the report, including the drill-downs.
4. Hide the Child group sections - in the gray area to the left of the sections, right-click and select "Hide". (There IS a difference between Suppress and Hide!)
5.
Suppress the details section unless users will drill down from child to transactions in which case you'll Hide the section.
You'll probably have to play with formatting in order to get the column headers set up correctly for each level of drill-down, but this should get you started.
-Dell