URL Formula to print report that shows related child records

Hello,

I need a URL formula that creates a print button, where the related project field in the child table is the [RECORD ID] of the parent record.

Currently I have this:

URLRoot() & "db/" & Dbid() &"?a=printr&rid=" & [Record ID#] & "&dfid=14"

This prints the child records report displayed on the parent form, however I need to print a different report from the child table, not the report I'm displaying on the parent record's form. 

Thank you in advance :)