Mass Updating Preferred Location on Matrix Children

We recently turned on Multi-Location Inventory and when that happened (among MANY other things), a new field was available on our item records.  The field is Preferred Location and drives what location initially gets populated on sales orders.  I did a csv import for every one of my items and every single Matrix Child record returns the result that the import completed with zero error, all the item records for matrix child records still have no value in Preferred Location.  I searched the Mass updates options and do not see Matrix items under the Items options.

Does anyone have any thoughts on what I may be able to do?