One method to do the latter:

use POSIX ":sys_wait_h";
SIG{CHLD} = \&REAPER;
sub REAPER {
  1 while (waitpid(-1,&WNOHANG) != -1);
  $SIG{CHLD} = \&REAPER;
}
[download]

On a somewhat off-topic note, what version of the perldocs (like this one) are the ones on PerlMonks? 5.6's waitpid docs have an example of exactly this, whereas 'tis missing on PerlMonks..
perl -e 'print "Just use $^X$\"$]!$/"'