It is easy to get these problems wrong, so I second using Parallel::ForkManager. In your solution you need to keep looping not only if there is more work to spawn, but also if there are children to reap. Update: That's confusing to read -- it just means you'll need to reap 3 children at the end.

I like to use a hash to maintain the children. Here's an untested solution, probably with bugs ...

use strict;
use warnings;

$SIG{CHLD} = 'IGNORE';
my $max_procs = 3;  # don't use strings when you want numbers
my @work = qw(fw1 fw2 fw3 fw4 fw5);
my %kids;
while (@work or keys %kids) {
   if (@work and $max_procs > keys %kids) {
      my $fw = shift @work;
      my $pid = fork;
      die "Can not fork!" if ! defined $pid;
      if ($pid) {
         $kids{$pid} = $fw;
      } else {
         exec "remotelogfile $fw logfile > /var/$fw.log";
         die;
      }
   } else {
     my $pid = waitpid(-1, 0);
     delete $kids{$pid};
   }
}
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