#!/usr/bin/env perl -l

use strict;
use warnings;
use autodie qw{:all};

use POSIX qw{WNOHANG};

my %children;

$SIG{CHLD} = sub {
    local ($!, $?);
    my $pid = waitpid(-1, WNOHANG);
    return if $pid == -1;
    return unless defined $children{$pid};
    delete $children{$pid};
    print "SIG{CHLD}: PID $pid ", kill(0 => $pid) ? 'NOT ' : '', 'reaped.';
};  

print "PARENT($$): Before multi_dir() call";

multi_dir();

sub multi_dir {
    for (0 .. 1) {
        my $pid = fork;
        die 'Undefined PID from fork()' unless defined $pid;

        if ($pid) { # parent
            $children{$pid} = 1;
            print "PARENT($$): Started child process with PID: $pid";
            print "PARENT($$): ", scalar keys %children, ' child processes';
        }
        else {      # child
            print "CHILD($$): New process started";
            system 'echo PPID=$PPID PID=$$; sleep 1';
            print "CHILD($$): system() finished";
        }

        exit;   # <<<=== PROBLEM HERE!
    }
}