I don't know how the Windows folks spawn their child processes, but in *nix, it's fork. For example:

my $pid = fork();
if ( ! defined $pid ) {
    die "Can't fork: $!\n";
}
if ( $pid ) {
    # parent
}
else {
    # child
}
[download]

You could also look at Proc::Daemon which has this and more wrapped up in a tidy package.

Using a file to do your communication is a fine idea. To avoid polling, you could also use signals to let the worker know when to look. Have a look at the "Signals" section of perlipc.