Returning the Position ID of the child of a Reference Parent

Hello all,

I am looking for suggestions on how to implement the following:

I have an Event hierarchy: child: e00, parent; e01.

I then have a Single Hier Selection measure (Promo Reference) along e01 at sku_e00 level, which indicates for a sku_event a Parent Event to be used for reference in a mapping.

I would like to write a rule so that on sku_e00 it returns the ID of any of the childs of the Parent Event selected in the SIngle Hier Selection.

To give an example:

We have the following Event structure:

child event 1, Parent Event 1