Nesting CHILDREFS formulas in child sheets enables multi-level data aggregations.

• In this example, “North America” contains SUM/CHILDREFS formulas aggregating values from its child sheets, “California” and “New York”.
• By demoting “North America” and its children, the SUM/CHILDREFS formulas on the parent sheet “NII Summary” automatically update to include the evaluated CHILDREFS formulas in the “North America” sheet.

Go here for Supplementary Info for CHILDREFS.