There are many ways you could do this, here is one using the Parallel::ForkManager module:

use Parallel::ForkManager;

use strict;
use warnings;

my $max = 50 # maximum number of children to create
my $pm  = new Parallel::ForkManager($max);

while(1) { # consider using "while(condition())" here instead
  # ...
  if (condition()) {
    my $pid = $pm->start and next;
    other();
    $pm->finish();
  }
}

sub other { # don't use capitalised subroutine names
  # ... whatever you want to do in the child
}
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Hope this helps