Oracle explain for cascading delete is wrong
I don't think this is possible.  

If I'm not mistaken, the optimizer doesn't even know (or at least doesn't try to know) that the statement will "touch" other tables as well.

It's not explicitely documented, but the following quote from the manual only talks about the tables "referenced" in the SQL statement (emphasis is mine):


The row source tree is the core of the execution plan. It shows the following information:
&nbsp;&nbsp;&nbsp;-&nbsp;&nbsp;An ordering of the tables referenced by the statement
&nbsp;&nbsp;&nbsp;-&nbsp;&nbsp;An access method for each table mentioned in the statement
...


I think the important part is: "tables referenced by the statement". No mentioning of "dependent" tables.

Edit:
If you need to extract that information, you probably have to trace your session and look at the TKPROF output.