CHILDREFS is more than a formula - it's a function you add to formulas to invoke data aggregation. Adding CHILDREFS to your formula tells the formula to apply the cell reference to all sheets that are children to the current sheet being edited in the outline. Changes to the outline structure will trigger the formula containing CHILDREFS to auto-update; no manual updating required.

In the above example, cell B10 contains the formula “=SUM(CHILDREFS(B10))”.

• Embedding the CHILDREFS function in the SUM formula tells the formula to SUM cells B10 in each sheet which is a child of “NII Summary”.
• Cell C10 contains an equivalent cross-sheet formula. (note how much longer the cross-sheet formula is).

In this example, we promote the sheet titled “North America” so it is no longer a child of “NII Summary”.

• Cell B10 in the “NII Summary” sheet automatically updated to not include the value in cell B10 on the “North America” sheet.
• Note cell C10 on the “NII Summary” sheet. This cross-sheet formula needs to be manually adjusted to remove the reference to the “North America” sheet.

Go here for more advanced examples of Combining CHILDREFs usages