Drill Down/ Call Report From a Report.

To call a report from a report follow the below mentioned steps.

1) Select event on which drill down report will execute i.e. button, trigger etc.
2) Select SRW package i.e. Srw.Run _Report
Srw.Run_Report('Report= Client_Dtl Batch=NO Client_Id=' :PF_CLIENT_ID );
Where Client_Dtl is the child report , :PF_CLIENT_ID is the parameter for child report.

Note: Be careful about the apace because here it works as a separator.