create parent after children

Hello Guys,
I need to create a postgres 7.3 (done that, its bundled with an app I
have to extend).
Now I need to create 2 tables one a table of events. usual mix of
column types, with varchar as primary key.

However when I get 3 events in with specific characteristics I need
to create a summary event saying " 3 events of type X received).

So I need I guess to create a foreign key in the table with the 3
events in, pointing to the primary key in the summary event table.
But normally the parent is created 1st then the children - so I am
confused now about what constraints to put where so i can ensure
things make sense.
any help appreciated..

Carlos