I fear your version does not work in parallel!
I just tested it with this variant:

$g=10;
$|=1;
for ($i=0; $i<$g; $i++) {
  pipe ($rh, $wh);         # both of these are generated in the loop
  if ($pid[$i]=fork()) {   # parent process
    waitpid($pid[$i], 0);  # wait for child
    close ($wh);
    while (<$rh>) {        # gimme the output
      if ($_ =~ m/^Error/) { push (@error, $_); }
      elsif ($_ =~ m/^Hits/) { push (@hits, $_); }
      else { push (@data, $_); }  # each is a result from an engine
    }
  }
  else {
    close ($rh);
    open (STDOUT, ">&$wh");
    $|=1;
    print "I will wait for ",$i+2," seconds\n";
    sleep $i+1;
    print "Good morning. I slept about ",$i+2," seconds\n";
    exit(0);
  }
}

print @data;
[download]

Two problems:

1. It really doesn't work in parallel
2. It doesn't give the output to the parent

It produces this output:

I will wait for 2 seconds
Good morning. I slept about 2 seconds
I will wait for 3 seconds
Good morning. I slept about 3 seconds
I will wait for 4 seconds
Good morning. I slept about 4 seconds
I will wait for 5 seconds
Good morning. I slept about 5 seconds
I will wait for 6 seconds
Good morning. I slept about 6 seconds
I will wait for 7 seconds
Good morning. I slept about 7 seconds
I will wait for 8 seconds
Good morning. I slept about 8 seconds
I will wait for 9 seconds
Good morning. I slept about 9 seconds
I will wait for 10 seconds
Good morning. I slept about 10 seconds
I will wait for 11 seconds
Good morning. I slept about 11 seconds
[download]

But the output should be something like this:

I will wait for 2 seconds
I will wait for 3 seconds
I will wait for 4 seconds
I will wait for 5 seconds
I will wait for 6 seconds
I will wait for 7 seconds
I will wait for 8 seconds
I will wait for 9 seconds
I will wait for 10 seconds
I will wait for 11 seconds
Good morning. I slept about 2 seconds
Good morning. I slept about 3 seconds
Good morning. I slept about 4 seconds
Good morning. I slept about 5 seconds
Good morning. I slept about 6 seconds
Good morning. I slept about 7 seconds
Good morning. I slept about 8 seconds
Good morning. I slept about 9 seconds
Good morning. I slept about 10 seconds
Good morning. I slept about 11 seconds
[download]

which I produced with a variant of my former version:

#!/usr/local/bin/perl
use warnings;
use strict;

my $children= 10;
my @out;
my $first_child;

$|=1;

my $pid= open($first_child, '-|');
if ($pid) {
    # parent
    @out= <$first_child>;
}
else {
    my(@child, @childpid);
    for (my $i=0; $i<$children; ++$i) {
        $childpid[$i]= open($child[$i], '|-');
        if ($childpid[$i]) {
            # do nothing yet
        }
        else {
            print "I will wait for ",$i+2," seconds\n";
            sleep $i+1;
            print "Good morning. I slept about ",$i+2," seconds\n";
            exit;
        }
    }
    foreach (@child) {
        close $_;
    }
    exit;
}

print @out;
[download]