trigger that needs a PK

Hi,
I'm sure this question has been ask before but I could not find anything on
google. I most likely did not enter the right text into the google search.

I have a parent table that requires that an insert into a child table happen.
The problem is I can not determine what the parent pk is for the insert into
the child because it hasn't happen yet - if I set the trigger to before
insert. So I guess I need something that works with after insert into the
parent so the pkid can be created.

The parent has:
pkid serial
lot varchar 30

the child:
pkid serial
fk_parent int
other fields....

The question is how can I get the pk and insert it into the child. Of course
I'm new so if I missed something just provide the link or tutorial.

Thanks in advance!

--
John Fabiani