Store the contents of the child packages in a table, say ETLChildPackages. Your master package would have a step that read the contents of this table (child package names) and...

Slight change to my original submission. If the interval is less than a week and the day of week is not found in that interval the following adjustments will need...

I think something like this is what you're looking for. I didn't do extensive testing as I wrote it at work. I hope it helps.

CREATE FUNCTION [dbo].[WeekdaysInInterval]

( @StartDate SMALLDATETIME,...