Hi Sravan,
unfortunately the delete=true only works on some stuff, and only some of the time, and does NOT work on custom objects, weather they are a parent or a sub.
Be very careful with the stored procedure as there is referential integrity to several tables not just the custom object table. Tables to watch out for are Security tables, process tables.
If you plan on writing delete statements for custom I recommend using SQL Trace to figure out what the app does. Keep in mind Support does not like direct deletes to the DB.
hope this helps.
Federico