## This would be my main script, and I'll keep it 
## fairly simple. Notice that I'm using a module 
## called ContinueBox. ContinueBox is trivial, but let's 
## say that ContinueBox maps to the your child script. It 
## contains the functionality that you want to be easily
## reused.

use strict;
use Tk;
use ContinueBox;

my $mw = MainWindow->new;
my $dialog = $mw->ContinueBox;

$mw->Button(
   -text => "start child",
   -command => sub {
      my $result = $dialog->Show;

      ## I'm not doing much with the result here
      ## but I could use it terminate the entire
      ## script if I wante if the result was "Exit".
      print "$result\n";
})->pack;

MainLoop;